Category · F20-F29 block
F28 — Other nonorganic psychotic disorders
Terminology note: F28 is a genuine, positively-described "doesn't fit the other boxes" category, not a place to put a case just because it is unusual or hard to think about. It requires enough information to describe an atypical psychotic picture, not an absence of information (that is F29's job — see the boundary card below).
What is this category?
F28 covers psychotic disorders that are clearly nonorganic (not explained by a diagnosed medical condition or substance use) and clearly do not meet the criteria for F20 through F25, but where enough is known about the presentation to describe a real, specific, atypical picture — for example, a persistent hallucinatory state without the delusions or thought disorder needed for F20, or a mixed picture that does not settle into any single category's pattern even after adequate observation.
Core diagnostic concept
The classification question F28 answers is: "is there a genuinely nonorganic psychotic picture, observed in enough detail, that clearly does not fit F20, F21, F22, F23, F24, or F25, but that can still be described as a specific presentation in its own right?" F28 requires positive, specific information about an atypical picture — it is not a shortcut for an unclear or under-observed case.
Key diagnostic features
- Confirmed nonorganic origin
- Organic conditions and substance use have been considered and reasonably excluded as the primary explanation.
- Does not meet F20-F25 criteria
- The presentation has been assessed against each of the block's other categories and does not fit any of them, even after adequate observation time.
- A describable, specific atypical picture
- Enough is known to characterise what the presentation actually looks like (for example, persistent hallucinations without a delusional system or thought disorder), even though it does not match a named category.
- Adequate observation has occurred
- F28 is reached after enough time and information have accumulated to reasonably rule out the other categories, not simply because the case is new or confusing.
How to weigh evidence
These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).
- supports A well-documented, months-long history of persistent auditory hallucinations without delusions, thought disorder, or mood symptoms, clearly nonorganic, not matching F20-F25's specific patterns.
- consistent not decisive Clinicians describe the case as 'atypical' or 'unusual.'
- raises alternative The case has only been observed for a few days, and it is simply too early to say it doesn't fit F20 or F23 yet.
- contradicts or weakens A medical or substance-related explanation has not yet been adequately investigated.
- missing and necessary to ask Whether enough time and information are actually available to positively describe the picture, or whether more observation is still needed.
Diagnostic boundary
F28 is distinguished from F29 by the amount and specificity of information available: F28 is used when enough is known to describe a real, specific, atypical picture that clearly doesn't fit F20-F25; F29 is used when a psychosis is confidently nonorganic but there simply is not enough information available to describe it more specifically, even as an atypical picture. F28 is distinguished from F20-F25 by having been checked against each of those categories' criteria and not matching any of them, rather than by symptom severity or drama.
Full comparisons:
Duration and course
Minimum duration: No fixed duration threshold applies to F28 itself; the requirement is adequate observation time to reasonably exclude F20-F25, which will vary by case.
Course: Course varies by the specific atypical picture involved and is not standardised the way F20 or F23's course patterns are.
Included presentations
- A persistent hallucinatory state without the delusions, thought disorder, or negative symptoms needed for F20, confirmed nonorganic, and not better explained by any other F20-F29 category.
- Other well-documented, specific nonorganic psychotic pictures that do not conform to F20 through F25 after adequate assessment.
Exclusions and distinguishing presentations
| If this is true instead… | Consider | Why |
|---|---|---|
| The case has not yet been observed long enough to confidently rule out F20 or F23 | F23 | Reassessment after further observation, rather than F28, is the better answer when the picture may still evolve into a recognised category. |
| There is genuinely not enough information available to describe even an atypical specific picture | F29 | F29 is the better fit when the case can only be confidently said to be 'nonorganic psychosis,' with no further specific description available. |
| An organic condition or substance use has not been adequately investigated or excluded | external capsule | F28 requires that organic and substance-related causes have been reasonably excluded, not merely assumed to be absent. |
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.
Common learner errors
Worked example — a specific but atypical picture
Grace, 58, has for the past eight months had persistent auditory hallucinations (hearing her late husband's voice offering reassurance) without ever developing delusions, thought disorder, negative symptoms, or a mood episode. A full medical work-up and substance history are unremarkable, and the pattern has remained essentially unchanged and clearly described across eight months of follow-up.
- Step 1 — Check organic and substance causes: a full medical work-up and substance history are unremarkable, reasonably excluding these explanations.
- Step 2 — Check each F20-F25 category in turn: no delusions or thought disorder for F20; no diffuse trait pattern for F21; no single fixed delusion for F22; no acute onset/brief course for F23; no relational induction for F24; no mood episode for F25.
- Step 3 — Check whether enough is known to describe a specific picture: yes — eight months of consistent, well-documented, isolated persistent hallucinations.
- Step 4 — Check observation adequacy: eight months is ample time to reasonably exclude the other categories rather than simply being an early or unclear presentation.
- Conclusion — F28 is best supported: a confirmed nonorganic, well-described, atypical psychotic picture that does not fit F20-F25.
Interactive practice
- Type A Eight months of one consistent, isolated feature Recognition / application · Foundation
- Type B Persistent, but no delusion at all Boundary / differential · Boundary
- Type C Unusual, but only six weeks in Insufficient information · Developing
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.
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What is the key difference between F28 and simply saying a case is 'confusing' or 'atypical'?
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.
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Why does F28 require adequate observation time before it can be applied?
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.
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Name the two conditions that must both be true before F28 is the best-supported answer.
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
F28: A confirmed nonorganic psychotic picture, observed in enough detail to describe specifically, that clearly does not fit F20 through F25.
Decisive boundary cues:
- Enough time/information to describe a specific atypical picture, all of F20-F25 reasonably excluded -> weighs toward F28.
- Too little time has passed to exclude F20 or F23 yet -> weighs toward provisional classification or reassessment, not F28.
- Confidently nonorganic but no specific description possible at all -> weighs toward F29 over F28.
Duration/course: No fixed threshold; adequate observation to reasonably exclude F20-F25 is what matters, not a specific number of weeks.
Nearest alternatives: F29, F23
Common mistake: Reaching for F28 as a default label for any case that feels unusual or hard to classify, rather than as a considered conclusion after checking each other category.
Retrieval prompt: Have I actually checked this against every other category in the block, and do I know enough to describe what this specifically looks like?
(or use your browser's print function) Open full-page printable revision view →
Related glossary terms
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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.
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Hallucination
A perceptual experience (in any sensory modality) that occurs without an external stimulus but is experienced as real.
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 F28 concepts; no verbatim CDDG or DCR text is reproduced.
Last reviewed: 2026-09-12. 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.