ICD-10 Code F99 – Mental disorder, not otherwise specified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code F99 – Mental disorder, not otherwise specified
What it is
F99 is a nonspecific diagnosis used when a mental disorder is documented, but the record does not identify a more precise condition. It signals an unspecified mental health problem rather than a defined psychiatric disorder.
Clinical signs
Clinical features vary; refer to documentation. You may see general psychiatric symptoms such as mood change, anxiety, behavioral disturbance, or impaired functioning without enough detail to assign a specific diagnosis.
When to use this code
Use F99 when the clinician documents a mental disorder but provides no further specification, and you cannot code a more exact condition. It may also apply when the note is too vague for a definite classification. Check documentation before defaulting to this code.
Do not use for
Do not use F99 when the chart supports a more specific mental disorder code, including mood, anxiety, psychotic, or substance-related diagnoses. Avoid using it as a placeholder when the documentation can be clarified.
Coding tip
Query the provider for a more specific diagnosis whenever the record only says “mental disorder” or “psychiatric condition.”