Category · F70-F79 block
F78 — Other mental retardation
Terminology note: ICD-10's own term for this block is "mental retardation." Modern clinical and educational usage prefers "intellectual disability" (used in DSM-5 and in ordinary clinical practice since the mid-2010s), and ICD-11 has renamed and relocated this entire classification territory to "disorders of intellectual development." This page keeps ICD-10's actual code and official title for classification accuracy, and uses person-first language throughout ("a person with an intellectual disability"), never a label standing in for the person.
What is this category?
F78 is a distinctive, block-specific category: it is used specifically when grading the degree of intellectual disability is made particularly difficult by an associated sensory, physical, or severe behavioural impairment that confounds standard assessment — not simply whenever assessment is inconvenient or incomplete for other reasons.
Core diagnostic concept
F78 applies when intellectual disability is evident, but an associated impairment — blindness, deafness, a severe physical disability, or a severe behavioural disorder, for example — specifically prevents the standard assessment methods from confidently placing the person into one of the F70-F73 severity grades. The key test is *why* a grade could not be confirmed: F78 requires that a specific, identifiable confound prevented confident grading, not merely that grading has not yet been attempted or that information happens to be missing (that situation is F79's territory instead — see the F78-vs-F79 differential).
Key diagnostic features
- Intellectual disability is evident
- There is no doubt that an intellectual disability is present — the difficulty is specifically in grading its severity.
- A specific, identifiable confound
- An associated sensory impairment (e.g. blindness, deafness), severe physical disability, or severe behavioural disorder that concretely prevents standard assessment methods from working as intended.
- Not simply missing information
- F78 requires that assessment was actually attempted and specifically confounded — not that it was never attempted or that a report is simply incomplete.
How to weigh evidence
These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).
- supports A documented attempt at standard assessment that specifically could not proceed as intended because of a severe associated sensory or behavioural impairment, with intellectual disability itself clearly evident from other observations.
- consistent not decisive An associated physical impairment is present, without any statement about whether it actually affected the assessment process.
- raises alternative No assessment has been attempted at all yet, and no reason is given for why grading is difficult — this points toward F79 instead.
- contradicts or weakens A grade was in fact successfully assigned elsewhere in the same record despite an associated impairment being present.
- missing and necessary to ask Whether an assessment was actually attempted, and if so, specifically what about it was confounded by the associated impairment.
Diagnostic boundary
F78 is distinguished from F70-F73 by whether a confident grade was actually achievable at all, and from F79 by whether the reason grading was not achieved is a specific, identifiable confound (F78) versus simply not enough information yet being available for any reason (F79).
Full comparisons:
Duration and course
Minimum duration: Onset during the developmental period, as with every category in this block.
Course: Not a duration-based distinction — the decisive factor is why a grade could not be confirmed.
Included presentations
- Intellectual disability clearly evident, with grading specifically prevented by an associated sensory, physical, or severe behavioural impairment that confounded standard assessment.
Exclusions and distinguishing presentations
| If this is true instead… | Consider | Why |
|---|---|---|
| No assessment attempted, and no specific reason given for the absence of a grade | F79 | F79 is the honest classification when information is simply insufficient for any reason, not specifically confounded by an identifiable impairment. |
Four-character subtypes (orientation)
As with every category in this block, the fourth character records behavioural impairment independently of the severity grade itself.
- F78.0 — No, or minimal, impairment of behaviour
- Behaviour does not require particular attention or treatment beyond the intellectual disability itself. (in_depth)
- F78.1 — Significant impairment of behaviour, requiring attention or treatment
- A behavioural disturbance (e.g. aggression, self-injury) significant enough to need its own dedicated attention, independent of the intellectual disability grade itself. (in_depth)
- F78.8 — Other impairments of behaviour
- A behavioural picture not fitting the other listed states. (taught for orientation only, not separately assessed in this pilot)
- F78.9 — Without mention of impairment of behaviour
- No information given about whether a behavioural impairment is present. (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.
Boundary capsule — The dual criteria and grading logic across F70-F79
A shared reasoning check for every category in this block: none of F70-F73 can be supported by an IQ score alone, none of them can be supported by an adaptive-functioning impression alone, and the severity grade (F70-F73) is a separate question from both the behavioural-impairment fourth character and from whether enough information exists to grade at all (F78 versus F79).
What to check:
- Both criteria, together: is there evidence of both significantly subnormal general intellectual functioning (an approximate IQ range) AND a matching concurrent deficit in adaptive functioning (communication, self-care, home living, social and community skills)? Either one alone, without the other, does not support an F70-F73 classification.
- Onset: has the pattern been present since the developmental period (conventionally, before adulthood), rather than appearing as a decline from a previously typical baseline later in life? A later, datable decline points toward an acquired dementia (F00-F03), not toward this block, however similar the resulting scores look.
- Severity grade versus behavioural-impairment axis: is the question 'how subnormal is intellectual and adaptive functioning' (F70 mild, F71 moderate, F72 severe, F73 profound) being kept separate from the independent fourth-character question 'is there also a significant behavioural impairment requiring its own attention or treatment' (.0-.9)? A significant behavioural impairment does not, by itself, make the severity grade any more or less severe.
- F78 versus F79: when a case cannot be graded into F70-F73, is that because grading is specifically confounded by an identifiable associated sensory, physical, or behavioural impairment that makes standard assessment difficult (points toward F78), or because there is genuinely insufficient information available to grade at all, with no such confound identified (points toward F79)? These are two different reasons for not grading, not interchangeable labels for 'unclear.'
A full standardized cognitive and adaptive-functioning assessment by a qualified professional, which is outside this capsule's scope and is needed before any of these classifications is used in real clinical, educational, or support-planning practice.
Worked example — a confound, not just missing information
A profoundly deaf and blind 7-year-old clearly shows global developmental delay and extensive daily-living support needs. A specialist team documents that standard intellectual assessment tools, which rely heavily on verbal and visual tasks, could not be meaningfully administered given his combined sensory impairments, despite repeated adapted attempts.
- Step 1 — Confirm intellectual disability is evident: global developmental delay and extensive support needs are clearly documented.
- Step 2 — Identify the specific confound: combined deafness and blindness specifically prevented standard assessment tools from working, despite genuine adapted attempts.
- Step 3 — Distinguish from F79: this is not simply missing information — a specific, identifiable reason for the confound is documented.
- Conclusion — F78 is supported: intellectual disability is evident, but grading is specifically prevented by an identifiable associated impairment, not merely unassessed.
Interactive practice
- Type A A confounding sensory impairment Recognition / application · Foundation
- Type B Hard to assess, or hard to know? Boundary discrimination · Transfer
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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State the specific test that separates F78 from F79.
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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Explain why the mere presence of an associated physical impairment is not, by itself, enough to support F78.
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
F78: Intellectual disability is evident, but a specific, identifiable associated impairment (sensory, physical, or severe behavioural) prevents confident grading.
Decisive boundary cues:
- A documented, specific confound preventing assessment -> weighs toward F78.
- No assessment attempted and no reason given -> weighs toward F79 instead.
- A grade successfully assigned despite an associated impairment -> weighs toward the relevant F70-F73 grade, not F78.
Duration/course: Not duration-based; the decisive factor is why grading was not achieved.
Nearest alternatives: F79, F72, F73
Common mistake: Assigning F78 whenever an associated physical impairment is present, without checking whether it actually confounded assessment.
Retrieval prompt: What specific confound, if any, is documented here as preventing a confident grade?
(or use your browser's print function) Open full-page printable revision view →
Related glossary terms
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Adaptive functioning
The practical skills a person uses to meet the everyday demands of independent living — communication, self-care, home living, social skills, use of community resources, self-direction, and similar domains — assessed relative to what is typically expected at a person's age and cultural context. A concurrent deficit in adaptive functioning, alongside subnormal intellectual functioning, is one of the two criteria required for an intellectual disability classification (F70-F73); intellectual functioning alone is never sufficient.
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 F70-F79; no verbatim CDDG or DCR text is reproduced. See Sources and Method for the full policy.
Last reviewed: 2026-09-17. 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. Intellectual disability is not the person — every person with an intellectual disability deserves the same dignity and respect as anyone else. If you are concerned about a child's development, or about an adult's intellectual or adaptive functioning, please speak with a qualified professional for assessment and support.