ICD-10 Code F09 – Unspecified mental disorder due to known physiological condition (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code F09 – Unspecified mental disorder due to known physiological condition
What it is
Use F09 for a mental disorder caused by a known physiological condition when the specific psychiatric diagnosis is not documented. It covers cognitive, behavioral, or emotional disturbance linked to an underlying medical cause.
Clinical signs
Clinical features vary; refer to documentation. Commonly noted findings include confusion, memory problems, personality change, mood disturbance, or other mental status changes associated with a physical condition.
When to use this code
Use this code when the provider documents a mental disorder due to a known physiological condition but does not specify the exact type. It is also appropriate when the chart supports a secondary mental disorder linked to another medical diagnosis and the record remains nonspecific.
Do not use for
Do not use F09 if the record identifies a more specific mental disorder, such as delirium, dementia, or psychotic disorder due to a medical condition. Check documentation if the cause is uncertain or if the condition is substance-related.
Coding tip
Code the underlying physiological condition first when documented, and use F09 only when the mental disorder is clearly linked but not further specified.