F99 — Mental disorder, not otherwise specified
F99 is a billable, specific ICD-10-CM code for mental disorder, not otherwise specified. It is valid for submission on a claim.
Excludes1 — never code together
These conditions cannot occur together. Billing both on the same encounter is a denial.
- unspecified mental disorder due to known physiological condition (F09)
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Mental illness NOS
Other codes that can never be billed with F99
These codes carry an Excludes1 note pointing at F99. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading F99 alone.
Risk adjustment
F99 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.
Medicare coverage
F99 is named in 5 Medicare coverage policies — 4 listing it as supporting medical necessity, and 1 listing it as NOT covered. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A52434Health and Behavior Assessment/Intervention – Medical Policy Articlenot covered
- A56756Billing and Coding: Home Health - Psychiatric Care
- A57480Billing and Coding: Psychiatry and Psychology Services
- A57520Billing and Coding: Psychiatric Diagnostic Evaluation and Psychotherapy Services
How F99 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to F99.
- Psychiatric disorder or problem
- Situation, psychiatric
- Aberration›mental
- Disease, diseased›mental
- Disease, diseased›psychiatric
- Disorder›mental(or behavioral) (nonpsychotic)
- Disorder›psychological
- Disturbance›mental
- Problem›psychiatric
- Reaction›psychogenic
Questions about F99
- Is F99 a billable ICD-10-CM code?
- Yes. F99 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does F99 sit in the tabular list?
- Mental, Behavioral and Neurodevelopmental disorders (F01-F99), in the block Unspecified mental disorder (F99).
- What cannot be coded together with F99?
- F99 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.