FY2027
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Excludes1 pair

F09 vs F99

F09 and F99 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.

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
  • 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