What is ICD-10 code F91.8?

F91.8 is the ICD-10-CM diagnosis code for Other conduct disorders. Behavioral or conduct disorders that do not fit the standard categories of family-confined, childhood-onset, adolescent-onset conduct disorder, or oppositional defiant disorder. It belongs to the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99). F91.8 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. F91.8 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. F91.8 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. F91.8 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for F91.8?

F91.8 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards F91.8 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

What should coders know when reporting F91.8?

Use only when conduct disorder is documented but does not meet criteria for other F91 codes Include detailed behavioral description in documentation to justify this classification

F91.8: Other conduct disorders — ICD-10

ICD-10-CM Code View

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Code lookupF91.8Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Mental, Behavioral and Neurodevelopmental disorders (F01-F99) / Behavioral and emotional disorders with onset usually occurring in childhood and adolescence (F90-F98)

F91.8

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Other conduct disorders

Behavioral or conduct disorders that do not fit the standard categories of family-confined, childhood-onset, adolescent-onset conduct disorder, or oppositional defiant disorder.

Buddy Insight

This code captures conduct disorders that are specifically identified but do not fit the standard subtypes (family-confined, childhood-onset, adolescent-onset, or oppositional defiant disorder).

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Not risk-adjusted for this model/period.

RAF 0

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Not risk-adjusted for this model/period.

RAF 0

RXHCC

Mapped

HCC 133

Personality Disorders, Anxiet...

RAF 0.0

Code Trumping

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Code Book Path

Official

F91Conduct disorders

F91.8Other conduct disorders

Inclusion Terms

Official

Other specified conduct disorder
Other specified disruptive disorder

Excludes 2

Official

conduct problems associated with attention-deficit hyperactivity disorder (F90.-)
mood [affective] disorders (F30-F39)
pervasive developmental disorders (F84.-)
schizophrenia (F20.-)

Related Child Codes

Official

F91.0Conduct disorder confined to family context

F91.1Conduct disorder, childhood-onset type

F91.2Conduct disorder, adolescent-onset type

F91.3Oppositional defiant disorder

F91.9Conduct disorder, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for F91.8 in this effective period.

Excludes 1

Official

antisocial behavior (Z72.81-)
antisocial personality disorder (F60.2)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for F91.8 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for F91.8 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for F91.8 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Provider documentation of a specific conduct disorder that does not fit standard subtype categories

Evidence of persistent behavioral pattern violating societal norms or others' rights

Clinical rationale for why standard subtypes are not applicable

Documentation of functional impairment

MEAT Support

HCC Buddy guidance

Provider documentation of a specific conduct disorder that does not fit standard subtype categories

Evidence of persistent behavioral pattern violating societal norms or others' rights

Clinical rationale for why standard subtypes are not applicable

Documentation of functional impairment

Audit Caution

HCC Buddy guidance

Using F91.8 when the presentation fits a standard conduct disorder subtype — always prefer specific subtypes

Confusing F91.8 with F91.9 — F91.8 requires documentation of specific features, F91.9 is for unspecified

Coding F91.8 without clinical rationale for why standard subtypes do not apply

Defaulting to F91.8 when the provider simply has not specified onset type — use F91.9 in that case

Common Mistakes

HCC Buddy guidance

F91.1 — Conduct disorder, childhood-onset type; use when symptoms began before age 10

F91.2 — Conduct disorder, adolescent-onset type; use when symptoms began in adolescence

F91.9 — Conduct disorder, unspecified; F91.8 is for a specific atypical presentation, while F91.9 is truly unspecified

F91.3 — Oppositional defiant disorder; ODD has its own code and should not be coded as F91.8

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is F91.8 an HCC code?

No. F91.8 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.

HCC Category Mapping

RxHCCHCC 133, Personality Disorders, Anxiety, and Other Specified Mental Disorders

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work F91.8 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for F91.8

For F91.8to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed F91.8 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

F91.8 is the ICD-10-CM diagnosis code for other conduct disorders. Behavioral or conduct disorders that do not fit the standard categories of family-confined, childhood-onset, adolescent-onset conduct disorder, or oppositional defiant disorder. F91.8 sits in the ICD-10-CM chapter for mental, behavioral and neurodevelopmental disorders (f01-f99), within the section covering behavioral and emotional disorders with onset usually occurring in childhood and adolescence (f90-f98).

F91.8 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

F91.8 does not map to any HCC in V28 or V24 models. RxHCC maps to 133 (0.000). No risk adjustment impact. Coders reviewing F91.8 should check whether additional documentation would support a more specific child code in the same hierarchy that does map to a payment HCC, capturing the correct specificity is the highest-impact RAF improvement available within accurate coding.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for F91.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use only when conduct disorder is documented but does not meet criteria for other F91 codes
•Include detailed behavioral description in documentation to justify this classification

Clinical Significance

This code captures conduct disorders that are specifically identified but do not fit the standard subtypes (family-confined, childhood-onset, adolescent-onset, or oppositional defiant disorder). This may include conduct disorders with atypical features or presentations that cross traditional subtype boundaries. Documentation should clearly specify the nature of the conduct disturbance.

Documentation Requirements

✓Provider documentation of a specific conduct disorder that does not fit standard subtype categories
✓Evidence of persistent behavioral pattern violating societal norms or others' rights
✓Clinical rationale for why standard subtypes are not applicable
✓Documentation of functional impairment
✓Treatment plan addressing the conduct disturbance

Commonly Confused Codes

•F91.1: Conduct disorder, childhood-onset type; use when symptoms began before age 10
•F91.2: Conduct disorder, adolescent-onset type; use when symptoms began in adolescence
•F91.9: Conduct disorder, unspecified; F91.8 is for a specific atypical presentation, while F91.9 is truly unspecified
•F91.3: Oppositional defiant disorder; ODD has its own code and should not be coded as F91.8