2026 ICD-10-CM Diagnosis Code R46.2Strange and inexplicable behavior

ICD-10-CM Codes›R00–R99›R40-R46›R46

ICD-10-CM R46.2
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

R46.2 is a billable ICD-10-CM diagnosis code for strange and inexplicable behavior. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. Coders also document this condition as behavior involving feces. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Symptoms of mental and substance use conditions.

Code Identity

ICD-10-CM Code
R46.2
Billable Status
Yes — Valid for Submission
Code Describes
Strange and inexplicable behavior
Short Description
Strange and inexplicable behavior
Same as the full description in the CMS dataset.
Parent Code
R46
Symptoms and signs involving appearance and behavior

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR40-R46Symptoms and signs involving cognition, perception, emotional state and behavior
CategoryR46Symptoms and signs involving appearance and behavior
This CodeR46.2Strange and inexplicable behavior

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Behavior involving feces
  • Bizarre behavior
  • Smearing of feces
  • Strange and inexplicable behavior

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.

    • Behavior
      • inexplicable
    • Behavior
      • strange (and inexplicable)

Clinical ClassificationClinical

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

CCSR SYM008
Symptoms of mental and substance use conditions
Default principal diagnosis: inpatient Yes · outpatient Yes

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 R46.2 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
799.89 Ill-define condition NEC
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 R46.2Overview

Is R46.2 (Symptoms and signs involving appearance and behavior) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report strange and inexplicable behavior on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can R46.2 be a principal diagnosis?

Use it with care. This is a symptom code, so once a definitive diagnosis explaining the strange and inexplicable behavior is established, that condition takes the principal position instead.

What is the ICD-9 equivalent of R46.2?

Under the General Equivalence Mappings, strange and inexplicable behavior converts to ICD-9-CM 799.89 (ill-define condition NEC). 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.