2027 ICD-10-CM Diagnosis Code F99Mental disorder, not otherwise specified
ICD-10-CM Codes›F01–F99›F99›F99
- Billable — Valid for Submission
- Not Chronic
F99 is a billable ICD-10-CM diagnosis code for mental disorder, not otherwise specified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 880. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Miscellaneous mental and behavioral disorders/conditions.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Axis I diagnosis
- Axis II diagnosis
- Axis III diagnosis
- Axis IV diagnosis
- Axis V diagnosis
- Brain fag
- Cheshire cat syndrome
- Chronic mental disorder
- Deferred diagnosis on Axis I
- Deferred diagnosis on Axis II
- Deferred diagnosis on Axis III
- Deferred diagnosis on Axis IV
- Deferred diagnosis on Axis V
- Ghost sickness
- Hypersomnia disorder related to another mental disorder
- Identity disorder
- Impairment of psychological status
- Insomnia disorder related to another mental disorder
- Mental disorder
- Mental disorder AND/OR culture bound syndrome
- Mental disorder during puerperium
- Mental disorder in infancy
- Mental disorder in mother complicating childbirth
- Mental disorder in mother complicating pregnancy
- Mental disorders during pregnancy, childbirth and the puerperium
- Not suitable for procedure
- Not suitable for procedure due to disease
- Not suitable for procedure due to mental disorder
- On severe mental illness register
- Psychiatric behavioral disability
- Psychiatric treatment changed
- Psychiatric treatment started
- Psychological disorder during pregnancy
- Root work
- Suspicion
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to F99: its own notes plus those printed at Chapter 5. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- disorders of psychological development
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Mental illness NOS
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- unspecified mental disorder due to known physiological condition (F09)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name F99, its category, or a range that includes it.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
mental F99
Disease, diseased See Also: Syndrome;
mental F99
psychiatric F99
Disorder (of) See Also: Disease;
Disturbance (s) See Also: Disease;
mental F99
Reaction See Also: Disorder;
psychogenic F99
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Mental Disorders
psychiatric illness or diseases manifested by breakdowns in the adaptational process expressed primarily as abnormalities of thought, feeling, and behavior producing either distress or impairment of function.
Patient EducationClinical
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..
The full article covers:
- What are mental disorders?
- What are some types of mental disorders?
- What causes mental disorders?
- Who is at risk for mental disorders?
- How are mental disorders diagnosed?
- What are the treatments for mental disorders?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert F99 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About F99Overview
What is the ICD-10 code for mental disorder, not otherwise specified?
The ICD-10-CM code for mental disorder, not otherwise specified is F99. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is F99 (Mental disorder, not otherwise specified) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report mental disorder, not otherwise specified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does F99 group to?
When mental disorder, not otherwise specified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 880 (acute Adjustment Reaction and Psychosocial Dysfunction), which carries a relative weight of 0.9306. Higher weights mean higher Medicare reimbursement.
Can F99 be reported with F09?
Not as a rule. The Excludes1 note on F99 lists "unspecified mental disorder due to known physiological condition (F09)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What is the ICD-9 equivalent of F99?
Under the General Equivalence Mappings, mental disorder, not otherwise specified converts to ICD-9-CM 300.9 (nonpsychotic disord NOS). The mapping is approximate, so confirm the match fits the documentation.
