2026 ICD-10-CM Diagnosis Code L51.9Erythema multiforme, unspecified

ICD-10-CM Codes›L00–L99›L49-L54›L51

ICD-10-CM L51.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

L51.9 is a billable ICD-10-CM diagnosis code for erythema multiforme, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 595 through 596. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Allergic reactions and Other specified inflammatory condition of skin.

Code Identity

ICD-10-CM Code
L51.9
Billable Status
Yes — Valid for Submission
Code Describes
Erythema multiforme, unspecified
Short Description
Erythema multiforme, unspecified
Same as the full description in the CMS dataset.
Parent Code
L51
Erythema multiforme

Code Classification

ChapterL00–L99Diseases of the skin and subcutaneous tissue
SectionL49-L54Urticaria and erythema
CategoryL51Erythema multiforme
This CodeL51.9Erythema multiforme, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Coccidioidomycosis with erythema multiforme
  • Drug-induced erythema multiforme
  • EMPACT syndrome
  • Erythema multiforme
  • Erythema multiforme co-occurrent with ulcer of oral mucous membrane
  • Erythema multiforme due to bacterial infection
  • Erythema multiforme due to Herpes simplex infection
  • Erythema multiforme due to malignancy
  • Erythema multiforme due to Mycoplasma pneumoniae infection
  • Erythema multiforme due to systemic fungal infection
  • Erythema multiforme due to viral disease
  • Erythema multiforme major
  • Erythema multiforme minor
  • Erythema multiforme of pregnancy
  • Erythema multiforme, dermal type
  • Erythema multiforme-induced ulceration of lips
  • Gingival disease due to erythema multiforme
  • Herpes iris
  • Lip ulcer
  • Mucous membrane erythema
  • Pregnancy eruption

Tabular List NotesGuidance

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

Inclusion Terms

  • Erythema iris
  • Erythema multiforme major NOS
  • Erythema multiforme minor NOS
  • Herpes iris

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.

    • Arthritis, arthritic(acute) (chronic) (nonpyogenic) (subacute)
      • in (due to)
        • erythema
          • multiforme
    • Arthropathy
      • in (due to)
        • erythema
          • multiforme
    • Erythema, erythematous(infectional) (inflammation)
      • iris
    • Erythema, erythematous(infectional) (inflammation)
      • multiforme (major) (minor)
    • Herpes, herpesvirus, herpetic
      • iris (vesicular erythema multiforme)

Clinical ClassificationClinical

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

CCSR INJ031
Allergic reactions
Default principal diagnosis: inpatient No · outpatient No
CCSR SKN002
Other specified inflammatory condition of skin
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Erythema Multiforme

    a skin and mucous membrane disease characterized by an eruption of macules, papules, nodules, vesicles, and/or bullae with characteristic bull's-eye lesions usually occurring on the dorsal aspect of the hands and forearms.

  • Erythema Multiforme Minor

    self-limiting form of erythema multiforme.

  • Erythema Multiforme Major

    a severe, sometimes life-threatening, form of erythema multiforme. it is considered to be a hypersensitivity skin reaction triggered by a variety of stimuli, including infections and medication. it is characterized by raised, edematous papules in the extremities; involvement of one or more mucous membranes; and epidermal detachment involving less than ten percent of the total body surface area.

Patient EducationClinical

Skin Conditions

Your skin is your body's largest organ. It covers the entire outside of your body. There are many ways that your skin protects your body and helps keep you healthy. For example, it:

The full article covers:

  • What does your skin do?
  • What problems and conditions can affect your skin?
  • How can I keep my skin healthy?

Read the full article at MedlinePlus

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

Convert L51.9 to ICD-9-CMHistory

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

ICD-9-CM
695.10 Erythema multiforme 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 L51.9Overview

Is L51.9 (Erythema multiforme) a billable code?

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

What MS-DRG does L51.9 group to?

When erythema multiforme, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 595, 596, with relative weights from 1.0825 to 2.1207 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of L51.9?

Under the General Equivalence Mappings, erythema multiforme, unspecified converts to ICD-9-CM 695.10 (erythema multiforme 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.