2026 ICD-10-CM Diagnosis Code E31.21Multiple endocrine neoplasia [MEN] type I

ICD-10-CM Codes›E00–E89›E20-E35›E31

ICD-10-CM E31.21
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

E31.21 is a billable ICD-10-CM diagnosis code for multiple endocrine neoplasia [MEN] type I. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 643 through 645. Coders also document this condition as multiple endocrine neoplasia, type 1. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified endocrine disorders.

Code Identity

ICD-10-CM Code
E31.21
Billable Status
Yes — Valid for Submission
Code Describes
Multiple endocrine neoplasia [MEN] type I
Short Description
Multiple endocrine neoplasia [MEN] type I
Same as the full description in the CMS dataset.
Parent Code
E31.2
Multiple endocrine neoplasia [MEN] syndromes

Code Classification

ChapterE00–E89Endocrine, nutritional and metabolic diseases
SectionE20-E35Disorders of other endocrine glands
CategoryE31Polyglandular dysfunction
This CodeE31.21Multiple endocrine neoplasia [MEN] type I

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Multiple endocrine neoplasia, type 1
  • Neoplasm of uncertain behavior of multiple endocrine glands
  • Polyglandular activity in multiple endocrine adenomatosis

Tabular List NotesGuidance

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

Inclusion Terms

  • Wermer's syndrome

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.

    • Disease, diseased
      • Wermer's
    • Neoplasia
      • endocrine, multiple (MEN)
        • type I
    • Syndrome
      • Wermer's
    • Wermer's disease or syndrome

Clinical ClassificationClinical

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

CCSR END015
Other specified and unspecified endocrine disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Multiple Endocrine Neoplasia Type 1

    a form of multiple endocrine neoplasia that is characterized by the combined occurrence of tumors in the parathyroid glands, the pituitary gland, and the pancreatic islets. the resulting clinical signs include hyperparathyroidism; hypercalcemia; hyperprolactinemia; cushing disease; gastrinoma; and zollinger-ellison syndrome. this disease is due to loss-of-function of the men1 gene, a tumor suppressor gene (genes, tumor suppressor) on chromosome 11 (locus: 11q13).

Patient EducationClinical

Endocrine Diseases

Your endocrine system includes eight major glands throughout your body. These glands make hormones. Hormones are chemical messengers. They travel through your bloodstream to tissues or organs. Hormones work slowly and affect body processes from head to toe. These include:

Read the full article at MedlinePlus

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

Convert E31.21 to ICD-9-CMHistory

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

ICD-9-CM
258.01 Mult endo neoplas type I
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 E31.21Overview

Is E31.21 (Multiple endocrine neoplasia [MEN] syndromes) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report multiple endocrine neoplasia [MEN] type I on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does E31.21 group to?

When multiple endocrine neoplasia [MEN] type I is the principal diagnosis on an inpatient stay, it groups to MS-DRG 643, 644, 645, with relative weights from 0.7683 to 1.6461 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of E31.21?

Under the General Equivalence Mappings, multiple endocrine neoplasia [MEN] type I converts to ICD-9-CM 258.01 (mult endo neoplas type I). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.