F09 vs F99
F09 and F99 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
The official note, declared on F99
unspecified mental disorder due to known physiological condition (F09)
F09
Unspecified mental disorder due to known physiological condition
BillableUnspecified
- Chapter 5
- Mental, Behavioral and Neurodevelopmental disorders
- Section
- F01-F09
Use when the record says
- Mental disorder NOS due to known physiological condition
- Organic brain syndrome NOS
- Organic mental disorder NOS
- Organic psychosis NOS
- Symptomatic psychosis NOS
Indexed under
- Deficiency, deficient › cognitive
- Disorder › cognitive (of)
- Organic › brain syndrome
- Organic › mental disorder
- Organic › psychosis
F99
Mental disorder, not otherwise specified
Billable
- Chapter 5
- Mental, Behavioral and Neurodevelopmental disorders
- Section
- F99
Use when the record says
- Mental illness NOS
Indexed under
- Psychiatric disorder or problem
- Situation, psychiatric
- Aberration › mental
- Disease, diseased › mental
- Disease, diseased › psychiatric
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027