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  6. 2025 ICD-10-CM Code F99

2025 ICD-10-CM Diagnosis Code F99

Mental disorder, not otherwise specified

ICD-10-CM Code:
F99
ICD-10 Code for:
Mental disorder, not otherwise specified
Is Billable?
Yes - Valid for Submission
Chronic Condition Indicator: [1]
Not chronic
Code Navigator:

F99 is a billable diagnosis code used to specify a medical diagnosis of mental disorder, not otherwise specified. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2024 through September 30, 2025.

Code Classification

  • Mental and behavioural disorders
    F01–F99
    • Unspecified mental disorder
      F99
      • Mental disorder, not otherwise specified
        F99

Approximate Synonyms

The following list of clinical terms are approximate synonyms, alternative descriptions, or common phrases that might be used by patients, healthcare providers, or medical coders to describe the same condition. These synonyms and related diagnosis terms are often used when searching for an ICD-10 code, especially when the exact medical terminology is unclear. Whether you're looking for lay terms, similar diagnosis names, or common language alternatives, this list can help guide you to the correct ICD-10 classification.

  • Axis I diagnosis
  • Axis II 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
  • Indication for modification of patient physical status
  • Indication for modification of patient psychological status
  • Indication for modification of patient status
  • Indication for modification of patient 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
  • Mental disorders during pregnancy, childbirth and the puerperium
  • On severe mental illness register
  • Pregnancy with mental disorders
  • Psychiatric behavioral disability
  • Psychiatric treatment changed
  • Psychiatric treatment started
  • Psychological disorder during pregnancy
  • Root work
  • Suspicion

Clinical Classification

Clinical Classifications group individual ICD-10-CM diagnosis codes into broader, clinically meaningful categories. These categories help simplify complex data by organizing related conditions under common clinical themes.

They are especially useful for data analysis, reporting, and clinical decision-making. Even when diagnosis codes differ, similar conditions can be grouped together based on their clinical relevance. Each category is assigned a unique CCSR code that represents a specific clinical concept, often tied to a body system or medical specialty.

Miscellaneous mental and behavioral disorders/conditions

CCSR Code: MBD013

Inpatient Default: Y - Yes, default inpatient assignment for principal diagnosis or first-listed diagnosis.

Outpatient Default: Y - Yes, default outpatient assignment for principal diagnosis or first-listed diagnosis.

Clinical Information

  • 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.

Tabular List of Diseases and Injuries

The following annotation back-references are applicable to this diagnosis code. The Tabular List of Diseases and Injuries is a list of ICD-10-CM codes, organized "head to toe" into chapters and sections with coding notes and guidance for inclusions, exclusions, descriptions and more.


Inclusion Terms

Inclusion Terms
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.
  • Mental illness NOS

Type 1 Excludes

Type 1 Excludes
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.
  • unspecified mental disorder due to known physiological condition F09

Index to Diseases and Injuries References

The following annotation back-references for this diagnosis code are found in the injuries and diseases index. The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10-CM code(s).

Convert F99 to ICD-9-CM

Below are the ICD-9 codes that most closely match this ICD-10 code, based on the General Equivalence Mappings (GEMs). This ICD-10 to ICD-9 crosswalk tool is helpful for coders who need to reference legacy diagnosis codes for audits, historical claims, or approximate code comparisons.

Nonpsychotic disord NOS

ICD-9-CM: 300.9

Approximate Flag - The approximate mapping means this ICD-10 code does not have an exact ICD-9 equivalent. The matched code is the closest available option, but it may not fully capture the original diagnosis or clinical intent.

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Patient Education


Mental Disorders

What are 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..

What are some types of mental disorders?

There are many different types of mental disorders. Some common ones include:

  • Anxiety disorders, including panic disorder, obsessive-compulsive disorder, and phobias
  • Depression, bipolar disorder, and other mood disorders
  • Eating disorders
  • Personality disorders
  • Post-traumatic stress disorder (PTSD)
  • Psychotic disorders, including schizophrenia

What causes mental disorders?

There is no single cause for mental illness. A number of factors can contribute to risk for mental illness, such as:

  • Your genes and family history
  • Your life experiences, such as stress or a history of abuse, especially if they happen in childhood
  • Biological factors such as chemical imbalances in the brain
  • A traumatic brain injury (TBI)
  • Prenatal (before birth) exposure to viruses, toxic chemicals, or other substances such as alcohol and drugs.
  • Use of alcohol or recreational drugs
  • Having a serious medical condition like cancer
  • Having few friends, and feeling lonely or isolated

Mental disorders are not caused by character flaws. They have nothing to do with being lazy or weak.

Who is at risk for mental disorders?

Mental disorders are common. Many Americans will be diagnosed with a mental disorder at some time in their life.

How are mental disorders diagnosed?

The steps to getting a diagnosis include:

  • A medical history
  • A physical exam and possibly lab tests, if your provider thinks that other medical conditions could be causing your symptoms
  • A psychological evaluation. You will answer questions about your thinking, feelings, and behaviors.

What are the treatments for mental disorders?

Treatment depends on which mental disorder you have and how serious it is. You and your provider will work on a treatment plan just for you. It usually involves some type of therapy. You may also take medicines. Some people also need social support and education on managing their condition.

In some cases, you may need more intensive treatment. You may need to go to a psychiatric hospital. This could be because your mental illness is severe. Or it could be because you are at risk of hurting yourself or someone else. In the hospital, you will get counseling, group discussions, and activities with mental health professionals and other patients.


[Learn More in MedlinePlus]

Code History

  • FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
  • FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
  • FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.

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.