Mental disorder, not otherwise specified
chapter 5: Mental, Behavioral and Neurodevelopmental Disorders
- F99 is billable and valid on claims for FY 2027.
- As a secondary diagnosis it is not a CC or MCC, so it doesn't raise the MS-DRG payment.
- Doesn't count toward a Medicare Advantage risk score (no HCC in V28).
- AHRQ's Chronic Condition Indicator classes it as not chronic (an acute or short-term condition).
- 24 US deaths in 2024 had an underlying cause in category F99, per the National Vital Statistics System on CDC WONDER. Death records use WHO ICD-10, so the count is for the whole category.
Also indexed as: Aberration, mental; Disease, mental; Disease, psychiatric; Disorder, mental; Disorder, psychological; Disturbance, mental; Problem, psychiatric; Psychiatric disorder or problem; Reaction, psychogenic; Situation
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Instructional notes
Includes: conditions that are coded here
- Mental illness NOS
Excludes1: not coded here, use a different code
- unspecified mental disorder due to known physiological condition (F09)
Official coding guidelines
From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.
Covers psychological pain disorders, substance use, abuse, dependence and remission, factitious disorder including Munchausen by proxy, and dementia severity.
- Pain disorders related to psychological factors (page 43)
- Mental and behavioral disorders due to psychoactive substance use (page 43)
- Factitious Disorder (page 44)
- Dementia (page 45)
F99 MS-DRG
As the principal diagnosis, F99 groups to MS-DRG 880 (v44.0).
Related conditions
Grouped by AHRQ's Clinical Classifications Software Refined (CCSR), which sorts every diagnosis code into clinically meaningful categories.
F99 is in Miscellaneous mental and behavioral disorders/conditions (MBD013, its default category), with 53 codes. Others in it:
- F06.8 Other specified mental disorders due to known physiological condition
- F07.9 Unspecified personality and behavioral disorder due to known physiological condition
- F09 Unspecified mental disorder due to known physiological condition
- F48.8 Other specified nonpsychotic mental disorders
- F48.9 Nonpsychotic mental disorder, unspecified
- F52.0 Hypoactive sexual desire disorder
- F52.1 Sexual aversion disorder
- F52.21 Male erectile disorder
Medicare coverage articles listing F99
These 4 Medicare billing and coding articles list F99 as a diagnosis that supports medical necessity for the services they cover. From the CMS Medicare Coverage Database; check your own contractor's article before billing.
Other codes that refer to F99
Notes on these codes point to F99.
- F29 Excludes1: mental disorder NOS (F99)
- O99.34 Includes: Conditions in F01-F09, F20-F52 and F54-F99
- R40-R46 Excludes2: symptoms and signs constituting part of a pattern of mental disorder (F01-F99)
- R46 Excludes1: mental and behavioral disorders (F01-F99)
- Z81.8 Includes: Conditions classifiable elsewhere in F01-F99
About the condition
Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.
Mental Disorders
Mental disorders (or mental illnesses) are conditions that affect your thinking, feeling, mood, and behavior. They may happen over a short period of time or come and go. Some can be chronic (long-lasting). They can affect your ability to relate to others and function each day..
Read more about mental disorders on MedlinePlusCode history
Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.
ICD-9-CM equivalent
Legacy crosswalk from the CMS General Equivalence Mappings (last updated 2018).
- 300.9 Unspecified nonpsychotic mental disorder (approximate)