2026 ICD-10-CM Diagnosis Code F99Mental disorder, not otherwise specified

ICD-10-CM Codes›F01–F99›F99›F99

ICD-10-CM F99
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Miscellaneous mental and behavioral disorders/conditions.

Code Identity

ICD-10-CM Code
F99
Billable Status
Yes — Valid for Submission
Code Describes
Mental disorder, not otherwise specified
Chapter
F99
Unspecified mental disorder

Code Classification

ChapterF01–F99Mental and behavioural disorders
SectionF99Unspecified mental disorder
CategoryF99Mental disorder, not otherwise specified
This CodeF99Mental disorder, not otherwise specified

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

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Aberration
      • mental
    • Disease, diseased
      • mental
    • Disease, diseased
      • psychiatric
    • Disorder(of)
      • mental (or behavioral) (nonpsychotic)
    • Disorder(of)
      • psychological
    • Disturbance(s)
      • mental
    • Problem(with) (related to)
      • psychiatric
    • Psychiatric disorder or problem
    • Reaction
      • psychogenic
    • Situation, psychiatric

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MBD013
Miscellaneous mental and behavioral disorders/conditions
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

ICD-9-CM
300.9 Nonpsychotic disord NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About F99Overview

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 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.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.