2026 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 2026 (October 1, 2025 through September 30, 2026) 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 II
- Deferred diagnosis on Axis III
- Female athlete triad
- 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
- On severe mental illness register
- Psychiatric behavioral disability
- Psychiatric treatment changed
- Psychiatric treatment started
- Psychological disorder during pregnancy
- Root work
- Suspicion
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Mental illness NOS
Type 1 Excludes
- unspecified mental disorder due to known physiological condition F09
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
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
Level of Suspicion|Index of Suspicion
refers to the likelihood that a diagnosis is accurate.Rate Overall Experience with Communication Related to Cancer Care|Overall, how would you rate your experiences with communication related to your cancer care, from the time there was a suspicion that you might have cancer, through the present
a question about how an individual would rate their experiences with communication related to their cancer care overall, from the time there was a suspicion that they might have cancer, through the present.Suspicion
an impression that something is possible or probable.Suspicion of Limb Electrodes Reversal But Interpretation Assumes No Reversal by ECG Finding|SUSPECT LIMB ELECTRODES REVERSED, INTERPRETATION ASSUMES NO REVERSAL
an electrocardiographic recording in which an interchange of one or more limb lead electrodes is suspected, but for which an interpretation is performed as though the lead placement is correct. (cdisc)Suspicion of Limb Electrodes Reversal But Interpretation Assumes Reversal by ECG Finding|SUSPECT LIMB ELECTRODES REVERSED, INTERPRETATION ASSUMES REVERSAL
an electrocardiographic recording in which an interchange of one or more limb lead electrodes is suspected, and for which an interpretation is performed as though the leads have in fact been interchanged. (cdisc)Suspicion of Metastasis|Suspicion of Metastases
an impression that a tumor has possibly spread from its original site of growth to another anatomic site.Rate Overall Experience with Communication Related to Cancer Care Question|Overall, how would you rate your experiences with communication related to your cancer care, from the time there was a suspicion that you might have cancer, through the present|Rate Overall Experience with Communication Related to Cancer Care
a question about how an individual would rate their experiences with communication related to their cancer care overall, from the time there was a suspicion that they might have cancer, through the present.
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, 2025 through September 30, 2026.
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, 2025 through September 30, 2026.
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 0.9602. Higher weights mean higher Medicare reimbursement.
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.
