2027 ICD-10-CM Diagnosis Code B01.11Varicella encephalitis and encephalomyelitis

ICD-10-CM Codes›A00–B99›B00-B09›B01

ICD-10-CM B01.11
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B01.11 is a billable ICD-10-CM diagnosis code for varicella encephalitis and encephalomyelitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 97 through 99, 791, 793. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 24 closely related codes. Coders also document this condition as post-infectious encephalitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encephalitis and Viral infection.

Code Identity

ICD-10-CM Code
B01.11
Billable Status
Yes — Valid for Submission
Code Describes
Varicella encephalitis and encephalomyelitis
Short Description
Varicella encephalitis and encephalomyelitis
Same as the full description in the CMS dataset.
Parent Code
B01.1
Varicella encephalitis, myelitis and encephalomyelitis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB01Varicella [chickenpox]
This CodeB01.11Varicella encephalitis and encephalomyelitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Post-infectious encephalitis
  • Postvaricella encephalitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B01.11: its own notes plus those printed at Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Postchickenpox encephalitis and encephalomyelitis

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name B01.11, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming B01.11: they are not reported together with it, unless the two conditions are unrelated.

  • G04.01 Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM)
    post chickenpox encephalitis (B01.1) names B01.1, which includes this code
  • G05 Encephalitis, myelitis and encephalomyelitis in diseases classified elsewhere
    postchickenpox encephalitis, myelitis and encephalomyelitis (B01.1-) names B01.1-, which includes this code

Excludes2 2

These codes carry an Excludes2 note naming B01.11: its condition is not part of those codes, and both may be reported when the patient has both.

  • B10 Other human herpesviruses
    human herpesvirus 3 (B01.-, B02.-) names B01.-, which includes this code
  • B10 Other human herpesviruses
    varicella (B01.-) names B01.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

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

CCSR NVS002
Encephalitis
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Chickenpox

Chickenpox is an infection caused by the varicella-zoster virus. Most cases are in children under age 15, but older children and adults can get it. It spreads very easily from one person to another.

Read the full article at MedlinePlus

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

Convert B01.11 to ICD-9-CMHistory

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

ICD-9-CM
052.0 Postvaricella encephalit
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About B01.11Overview

What is the ICD-10 code for varicella encephalitis and encephalomyelitis?

The ICD-10-CM code for varicella encephalitis and encephalomyelitis is B01.11 (sometimes written as B0111). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is B01.11 (Varicella encephalitis, myelitis and encephalomyelitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report varicella encephalitis and encephalomyelitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does B01.11 group to?

When varicella encephalitis and encephalomyelitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 98, 99, 97, with relative weights from 1.5249 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.

Is B01.11 a CC or MCC?

CMS lists B01.11 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 24 closely related codes in its exclusion list.

What is the ICD-9 equivalent of B01.11?

Under the General Equivalence Mappings, varicella encephalitis and encephalomyelitis converts to ICD-9-CM 052.0 (postvaricella encephalit). The mapping is approximate, so confirm the match fits the documentation.