Category · F20-F29 block
F20 — Schizophrenia
Terminology note: "Schizophrenia" is the official ICD-10 title and remains standard clinical and classification terminology; it is not a legacy term requiring a contemporary substitute. Colloquial misuse of the word (e.g. to mean "split personality" or unpredictable behaviour) is inaccurate and is corrected in the glossary.
What is this category?
Schizophrenia is a category for a psychotic illness in which thinking, perception, affect and sense of self can all be disturbed, over a sustained period, without the disturbance being adequately explained by an organic brain condition, a psychoactive substance, or a mood episode. It is the anchor category of the F20-F29 block: most of the other categories in the block exist to describe presentations that resemble schizophrenia but differ from it in duration, course, or the relative weight of mood symptoms.
Core diagnostic concept
The classification question F20 answers is not "does this person have unusual beliefs or experiences?" but "is there a sustained pattern of characteristic psychotic disturbance, lasting long enough and clear enough to distinguish it from a brief reaction, a mood episode with psychotic features, or an organic/substance-induced state?" Schizophrenia is defined educationally here as a sustained pattern, not a single symptom, and not a personality trait.
Key diagnostic features
- Passivity and thought-interference experiences
- Experiences of thoughts being read, inserted, withdrawn or broadcast, or of actions/feelings being controlled by an outside force. These are given substantial classificatory weight because they are relatively distinctive to this group of disorders.
- Auditory hallucinations with a specific quality
- Voices commenting on the person's actions in the third person, voices discussing the person, or other clearly abnormal auditory hallucinations, as opposed to a single vague or fleeting auditory experience.
- Persistent, culturally inappropriate delusions
- Fixed false beliefs that are bizarre or completely implausible within the person's cultural context (for example, being able to control the weather), held with conviction and not adequately explained by mood state.
- Formal thought disorder
- Breaks or interpolations in the flow of thought producing incoherent or irrelevant speech, or neologisms — disturbance in the structure of thinking itself, not merely its content.
- Catatonic behaviour
- Marked psychomotor disturbance such as stupor, mutism, waxy flexibility, negativism or excitement.
- Negative symptoms
- Marked apathy, poverty of speech, blunted or incongruous affect, and social withdrawal, usually leading to social decline — provided these are not caused by depression or medication.
- Significant and consistent change in overall behaviour
- Loss of interest, aimlessness, self-absorption and social withdrawal, evident as a change from the person's baseline functioning.
How to weigh evidence
These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).
- supports Clear third-person running-commentary voices, present most days for a month.
- consistent not decisive Social withdrawal alone, without other psychotic features.
- raises alternative Psychotic symptoms that began within days of stimulant use.
- contradicts or weakens Symptoms present for only four days with full recovery and no history of a longer episode.
- missing and necessary to ask Whether the psychotic features occurred only during a manic or depressive episode.
Diagnostic boundary
F20 is distinguished from its nearest neighbours mainly by three variables: duration and course (against F23), the centrality of mood (against F25 and affective disorders with psychotic features), and whether there is one circumscribed belief system rather than a broader disturbance (against F22 and F21). See the linked comparisons for the full reasoning.
Full comparisons:
Duration and course
Minimum duration: Characteristic psychotic symptoms should have been clearly present for most of the time during an episode of psychotic illness lasting at least one month (or for some of the time during most days within that period).
Course: Course is variable and is not part of the defining criterion in the same way duration is: schizophrenia in this classification can be a single episode, a relapsing-remitting pattern, or a more continuous course. Course descriptors are a secondary, subtype-level refinement (see subcategories) rather than the primary boundary against neighbouring categories.
Included presentations
- A sustained illness with prominent positive symptoms (delusions, hallucinations, thought disorder) meeting the duration rule.
- A sustained illness in which negative symptoms and behavioural decline dominate, once organic, substance and mood explanations are excluded.
- Presentations with marked catatonic features occurring within a broader schizophrenic illness.
Exclusions and distinguishing presentations
| If this is true instead… | Consider | Why |
|---|---|---|
| Symptoms lasting less than one month with recovery | F23 | Duration is not met; consider an acute and transient psychotic disorder instead. |
| Psychotic symptoms occurring only during a clearly established manic or depressive episode | affective disorders capsule | Mood disorder with psychotic features should be considered before F20 when psychosis is confined to mood episodes. |
| Prominent, roughly simultaneous mood and psychotic symptoms of comparable weight, recurring together | F25 | Schizoaffective disorder is the more specific category when both symptom clusters are prominent within the same episode. |
| One well-organised, non-bizarre delusion (or a related belief system) with little other disturbance | F22 | Persistent delusional disorder is narrower and does not require the broader schizophrenic symptom picture. |
| A lifelong pattern of eccentric thinking, odd beliefs and social discomfort without a sustained frank psychotic episode | F21 | Schizotypal disorder describes an enduring pattern rather than an episode of illness. |
| Clear evidence of an organic brain condition, or onset temporally linked to substance intoxication, withdrawal, or a prescribed medication | organic substance capsule | F20-F29 categories require that the disturbance is not better explained by an organic or substance-related cause. |
Four-character subtypes (orientation)
A learner should not select a subtype from a single striking feature (for example, calling any paranoid-sounding case "paranoid schizophrenia") without checking which cluster of features predominates across the presentation as a whole. Subtype classification is taught here for orientation only and is not separately assessed in this pilot.
- F20.0 — Paranoid schizophrenia
- Relatively stable, often paranoid, delusions usually accompanied by hallucinations; disturbances of affect, volition and speech, and catatonic symptoms, are comparatively less prominent. (taught for orientation only, not separately assessed in this pilot)
- F20.1 — Hebephrenic schizophrenia
- Affective changes are prominent, delusions and hallucinations fleeting and fragmentary, behaviour irresponsible and unpredictable, and thought disorganised; onset usually in adolescence or young adulthood. (taught for orientation only, not separately assessed in this pilot)
- F20.2 — Catatonic schizophrenia
- Prominent psychomotor disturbances dominate the clinical picture (stupor, excitement, posturing, negativism, rigidity, waxy flexibility, command automatism). (taught for orientation only, not separately assessed in this pilot)
- F20.3 — Undifferentiated schizophrenia
- Meets the general criteria for F20 but does not conform to any single subtype pattern, or shows features of more than one without a clear predominance. (taught for orientation only, not separately assessed in this pilot)
- F20.5 — Residual schizophrenia
- A chronic stage in which negative symptoms predominate following at least one clear-cut past psychotic episode, with earlier positive symptoms now much reduced. (taught for orientation only, not separately assessed in this pilot)
- F20.6 — Simple schizophrenia
- Insidious and progressive development of negative symptoms and social decline without a preceding history of overt psychotic episodes. (taught for orientation only, not separately assessed in this pilot)
External causes to check first
Categories in this block require that the disturbance is not better explained by another external cause listed below. These short capsules are reminders, not full teaching modules.
External cause capsule — Organic or medical causes
A reminder that F20-F29 categories require ruling out an organic brain condition before applying a primary psychiatric classification; this is not a full teaching module on organic mental disorders (see the F00-F09 block, planned).
What to check:
- Onset in the context of a known neurological condition (e.g. epilepsy, stroke, brain tumour, autoimmune encephalitis) or a general medical illness affecting the brain.
- New focal neurological signs, seizures, marked confusion, or fluctuating consciousness accompanying the psychotic features.
- Age of onset outside the usual range for a first psychotic episode, especially later-life onset without a prior psychiatric history.
- Rapid cognitive decline alongside psychotic symptoms.
A full organic-mental-disorder teaching module (F00-F09), which is outside this pilot's scope.
External cause capsule — Substance- or medication-related presentations
A reminder that psychotic symptoms temporally linked to substance use, intoxication, withdrawal, or medication require consideration of a substance-induced explanation before an F20-F29 category is applied.
What to check:
- Timing: did the psychotic symptoms begin during or shortly after intoxication or withdrawal from a psychoactive substance?
- Type of substance: stimulants, cannabis, hallucinogens, alcohol withdrawal, and some prescribed medications (e.g. corticosteroids, certain dopaminergic agents) are recognised in general clinical teaching as capable of producing psychotic symptoms.
- Course after the substance is stopped: substance-induced psychosis typically improves within days to a few weeks of abstinence, though this is not absolute.
- Whether psychotic symptoms were present before any substance use began, which would argue against a purely substance-induced explanation.
A full teaching module on F10-F19 (substance-related disorders), which is on this product's expansion roadmap.
External cause capsule — Affective disorders with psychotic features
A reminder to check whether psychotic symptoms are confined to, and explained by, a manic or depressive episode, before applying F20 or F25.
What to check:
- Whether psychotic symptoms (e.g. mood-congruent delusions of guilt or grandiosity) appear only during a clearly established manic or depressive episode and resolve as the mood episode resolves.
- Whether mood symptoms clearly preceded the psychotic features, or vice versa.
- Whether the delusional content is mood-congruent (fitting the prevailing mood, e.g. grandiose ideas during mania) rather than the more mood-neutral or bizarre content typical of F20.
- Whether this pattern has recurred across more than one episode, which would raise consideration of F25 rather than a simple mood disorder with psychotic features.
The full F30-F39 category pages (F30, F31, F32, F33) themselves, which cover the severity-and-psychotic-features gradient for manic and depressive episodes in depth; this capsule is a focused reminder of the boundary against F20/F25, not a substitute for those pages.
External cause capsule — Delirium and disturbances of consciousness
A reminder to distinguish a disturbance of consciousness and attention (delirium) from a primary psychotic disorder, since delirium can present with hallucinations and delusion-like beliefs.
What to check:
- Level of consciousness and attention: delirium involves fluctuating, reduced clarity of awareness and impaired attention, which is not a feature of F20-F29 categories.
- Time course within a day: delirium symptoms characteristically fluctuate over hours, often worse at night, whereas F20-F29 presentations are typically more stable across a day.
- An identifiable acute medical trigger (infection, metabolic disturbance, medication effect, withdrawal) is common in delirium.
- Onset: delirium is usually acute (hours to days), which should also prompt consideration of F23 versus a purely medical explanation.
A full teaching module on delirium and organic mental disorders (F00-F09), which is outside this pilot's scope.
Common learner errors
Worked example — using duration and mood relationship together
A 24-year-old presents with a two-month history of hearing two voices that discuss him in the third person and comment on his actions, alongside a fixed belief that a local radio station is broadcasting his thoughts. His family reports he has become withdrawn, stopped attending classes, and shows little facial expression. There is no history suggesting a manic or depressive episode, no relevant substance use, and no medical illness identified.
- Step 1 — Check duration: symptoms have been present for about two months, most days, which satisfies the one-month minimum used to separate F20 from F23.
- Step 2 — Check for a mood explanation: no manic or depressive episode is described, and the psychotic features are not confined to a mood episode, which weighs against F25 or an affective disorder with psychotic features.
- Step 3 — Check breadth of disturbance: there is more than one fixed belief theme plus third-person commentary voices plus negative symptoms (blunted affect, withdrawal, functional decline) — a broader picture than a single circumscribed delusion, which weighs against F22.
- Step 4 — Check for organic/substance causes: none reported; if this vignette is being used for real teaching, the absence of a medical work-up should itself be flagged as missing information in a real clinical context, even though it is stipulated as absent here for classification purposes.
- Conclusion — The presentation is best classified as F20, supported by duration, breadth of disturbance, and lack of a mood or external explanation, while the boundary against F23, F25 and F22 has been explicitly checked rather than assumed.
Interactive practice
- Type A A change over two months Recognition / application · Foundation
- Type B Odd for years, or newly unwell? Boundary / differential · Boundary
- Type C One week in Insufficient information · Developing
- Type D New information changes the picture Progressive revision · Transfer
- Type E Just one voice Misconception correction · Foundation
- Type F Sorting the evidence Explanation and evidence selection · Boundary
Retrieval prompts
Try answering each of these from memory before revealing where to check. Nothing you think or type here is sent or saved anywhere.
-
Without looking back at the page, state the one piece of duration information that most often separates F20 from F23.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
-
Name one feature that would make you seriously consider F25 instead of F20.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
-
Explain in one sentence why a single unusual belief is not, by itself, enough to classify a case as F20.
Reveal answer location
Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
These self-checks are a personal study aid only, visible to you on this page for this visit — they are not stored and do not affect your mastery dimensions.
Rapid revision card
F20: A sustained (>= 1 month) psychotic illness with characteristic disturbances of thought, perception and affect, not better explained by mood, organic, or substance causes.
Decisive boundary cues:
- Duration >= 1 month, most of the time -> weighs toward F20 over F23.
- Mood symptoms confined to episodes and not central -> weighs toward F20 over F25/affective psychosis.
- Broad disturbance rather than one fixed belief -> weighs toward F20 over F22.
Duration/course: At least one month of characteristic symptoms, most of the time.
Nearest alternatives: F21, F22, F23, F25
Common mistake: Classifying from one dramatic symptom (a single hallucination or delusion) without checking duration, mood relationship, or external causes.
Retrieval prompt: What single question would you ask first to separate this case from F23?
(or use your browser's print function) Open full-page printable revision view →
Related glossary terms
-
Psychosis
A general descriptive term for a mental state in which a person's grasp of reality is significantly disturbed — typically through delusions, hallucinations, or marked thought disorder. Psychosis is a feature that can occur across many different categories, not a diagnosis in itself.
-
Delusion
A fixed, false belief that is firmly held despite clear evidence to the contrary, and that is not accounted for by the person's cultural or religious background.
-
Hallucination
A perceptual experience (in any sensory modality) that occurs without an external stimulus but is experienced as real.
-
Negative symptoms
A reduction or loss of normal functions — such as blunted affect, poverty of speech, apathy, and social withdrawal — as distinct from 'positive' symptoms like delusions and hallucinations, which are additions to normal experience.
-
Insight (clinical)
The degree to which a person recognises that their experiences (such as unusual beliefs or perceptions) may reflect an illness rather than external reality. Insight can vary and is not itself a classification criterion, but is often noted educationally.
-
Thought insertion (and related passivity experiences)
The experience that thoughts are being placed into one's mind by an external agency (related experiences include thought withdrawal, thought broadcast, and passivity of action/feeling — the sense that one's actions or feelings are controlled from outside).
-
Affect
The observable expression of emotion (facial expression, tone of voice, gesture) at a given moment, as distinct from mood, which refers to a more sustained emotional state.
Source basis
WHO ICD-10 international classification structure and code/title (ICD-10 Browser, 2019 English release).
Original educational synthesis, informed by general published clinical-education understanding of ICD-10 F20 criteria; no verbatim CDDG or DCR text is reproduced. See Sources and Method for the full policy.
Last reviewed: 2026-09-06. Full policy: Sources and Method.
Educational resource only. This page and its cases teach ICD-10 classification reasoning using fictional scenarios. It does not diagnose real people and should not be used to assess yourself or anyone else.