F99 — Mental disorder, not otherwise specified
Is F99 billable?
Yes — F99 is billable for FY2027. F99 is a valid, billable ICD-10-CM code at the highest level of specificity in its branch. F99 may be submitted for encounters from October 1, 2026 through September 30, 2027.
F99 at a glance
| Code | F99 |
|---|---|
| Description | Mental disorder, not otherwise specified |
| Billable | Yes |
| Code set | ICD-10-CM FY2027 |
| Valid for encounters | October 1, 2026 – September 30, 2027 |
Which MS-DRGs does F99 group to?
F99 sits in MDC 19 and helps define the logic of 1 MS-DRG (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.
- 880Acute Adjustment Reaction and Psychosocial Dysfunctionmedical
How is F99 listed in the Alphabetic Index?
These are the routes through the Alphabetic Index that lead to F99. They show the wording a clinician may have documented, which often differs from the Tabular description.
- Psychiatric disorder or problem
- Situation, psychiatric
- Aberration › mental
- Disease, diseased › mental
- Disease, diseased › psychiatric
- Disorder › mental (of)
- Disorder › psychological (of)
- Disturbance › mental (s)
- Problem › psychiatric (with) (related to)
- Reaction › psychogenic
Excludes1 — never code together
The conditions below can never be reported together with F99 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.
- unspecified mental disorder due to known physiological condition (F09)
Inclusion terms
Alternative wording in documentation that is classified to F99.
- Mental illness NOS
Excludes2 — not included here — inherited from Chapter 5
The conditions below are not part of F99, but a patient may have both at the same time. When documentation supports it, F99 and the excluded code may both be reported.
- symptoms, signs and abnormal clinical laboratory findings, not elsewhere classified (R00-R99)
How long has F99 existed?
F99 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.
Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.
Which codes are confused with F99?
ICD-10-CM declares these codes mutually exclusive with F99 — exactly one of each pair can be correct for a given encounter.