2026 ICD-10-CM Diagnosis Code N64.1Fat necrosis of breast

ICD-10-CM Codes›N00–N99›N60-N65›N64

ICD-10-CM N64.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

N64.1 is a billable ICD-10-CM diagnosis code for fat necrosis of breast. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 600 through 601. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as bilateral fat necrosis of breasts. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Nonmalignant breast conditions.

This medical diagnosis code is frequently used in OB/GYN medical specialties to designate conditions such lump in breast and other disorders of the breast.

Code Identity

ICD-10-CM Code
N64.1
Billable Status
Yes — Valid for Submission
Code Describes
Fat necrosis of breast
Short Description
Fat necrosis of breast
Same as the full description in the CMS dataset.
Parent Code
N64
Other disorders of breast

Code Classification

ChapterN00–N99Diseases of the genitourinary system
SectionN60-N65Disorders of breast
CategoryN64Other disorders of breast
This CodeN64.1Fat necrosis of breast

Code EditsBilling

Medicare Code Editor checks that affect claim validity for N64.1.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral fat necrosis of breasts
  • Fat necrosis of breast
  • Fat necrosis of left breast
  • Fat necrosis of right breast

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Fat necrosis (segmental) of breast

Code First

  • breast necrosis due to breast graft T85.898

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.

    • Fat
      • necrosis
        • breast
    • Necrosis, necrotic(ischemic)
      • breast (aseptic) (fat) (segmental)
    • Necrosis, necrotic(ischemic)
      • fat, fatty (generalized)
        • breast (aseptic) (segmental)
    • Necrosis, necrotic(ischemic)
      • mammary gland (fat) (segmental)

Clinical ClassificationClinical

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

CCSR GEN017
Nonmalignant breast conditions
Default principal diagnosis: inpatient No · outpatient Yes

Patient EducationClinical

Breast Diseases

Breast diseases include various conditions and changes in your breast. Most women experience breast changes at some time. Your age, hormone levels, and medicines you take may cause lumps, bumps, and discharges of fluids that are not breast milk.

The full article covers:

  • What are breast diseases?
  • What are the symptoms of breast disease?
  • How are breast diseases diagnosed?
  • What are the treatments for breast disease?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert N64.1 to ICD-9-CMHistory

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

ICD-9-CM
611.3 Fat necrosis of breast
Exact Match The mapping is direct, with no qualifiers.

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 N64.1Overview

Is N64.1 (Other disorders of breast) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fat necrosis of breast on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does N64.1 group to?

On inpatient claims, fat necrosis of breast maps to MS-DRG 600, 601, with relative weights from 0.6050 to 1.0416 depending on complications. Higher weights mean higher Medicare reimbursement.

Can N64.1 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because fat necrosis of breast describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

What is the ICD-9 equivalent of N64.1?

Under the General Equivalence Mappings, fat necrosis of breast converts to ICD-9-CM 611.3 (fat necrosis of breast). The mapping is a direct match.

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.