2027 ICD-10-CM Diagnosis Code G21.0Malignant neuroleptic syndrome

ICD-10-CM Codes›G00–G99›G20-G26›G21

ICD-10-CM G21.0
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G21.0 is a billable ICD-10-CM diagnosis code for malignant neuroleptic syndrome. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 91 through 93. 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 59 closely related codes. Coders also document this condition as neuroleptic malignant syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Drug induced or toxic related condition and Other nervous system disorders (often hereditary or degenerative).

Code Identity

ICD-10-CM Code
G21.0
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neuroleptic syndrome
Short Description
Malignant neuroleptic syndrome
Same as the full description in the CMS dataset.
Parent Code
G21
Secondary parkinsonism

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG20-G26Extrapyramidal and movement disorders
CategoryG21Secondary parkinsonism
This CodeG21.0Malignant neuroleptic syndrome

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Neuroleptic malignant syndrome

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G21.0: its own notes plus those printed at G21 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

On G21.0 itself
  • neuroleptic induced parkinsonism (G21.11)
From G21 Secondary parkinsonism applies to 8 codes
  • Huntington's disease (G10)
  • neurocognitive disorder with Lewy bodies (G31.83)
  • Shy-Drager syndrome (G90.3)
  • syphilitic Parkinsonism (A52.19)

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 6 (G00-G99) Diseases of the nervous system applies to 700 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Use Additional Code

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

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name G21.0, its category, or a range that includes it.

Excludes1 3

These codes carry an Excludes1 note naming G21.0: they are not reported together with it, unless the two conditions are unrelated.

  • G21.11 Neuroleptic induced parkinsonism
    malignant neuroleptic syndrome (G21.0)
  • G20.C Parkinsonism, unspecified
    secondary parkinsonism (G21.-) names G21.-, which includes this code
  • R25 Abnormal involuntary movements
    specific movement disorders (G20-G26) names G20-G26, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming G21.0: its condition is not part of those codes, and both may be reported when the patient has both.

  • F98.4 Stereotyped movement disorders
    movement disorders of organic origin (G20-G25) names G20-G25, 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 INJ030
Drug induced or toxic related condition
Default principal diagnosis: inpatient No · outpatient No
CCSR NVS006
Other nervous system disorders (often hereditary or degenerative)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Neuroleptic Malignant Syndrome

    a rare, life-threatening disorder that is caused by neuroleptic medications. it is characterized by fever, muscular cramps and rigidity, autonomic nervous system dysfunction, and changes in the mental status that may lead to coma.

  • Parkinson Disease, Secondary

    conditions which feature clinical manifestations resembling primary parkinson disease that are caused by a known or suspected condition. examples include parkinsonism caused by vascular injury, drugs, trauma, toxin exposure, neoplasms, infections and degenerative or hereditary conditions. clinical features may include bradykinesia, rigidity, parkinsonian gait, and masked facies. in general, tremor is less prominent in secondary parkinsonism than in the primary form. (from joynt, clinical neurology, 1998, ch38, pp39-42)

Patient EducationClinical

Drug Reactions

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.

The full article covers:

  • What is a drug interaction?
  • What are side effects?
  • What are drug allergies?
  • How can I stay safe when taking medicines?

Read the full article at MedlinePlus

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

Convert G21.0 to ICD-9-CMHistory

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

ICD-9-CM
333.92 Neuroleptic malgnt synd
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G21.0Overview

What is the ICD-10 code for malignant neuroleptic syndrome?

The ICD-10-CM code for malignant neuroleptic syndrome is G21.0 (sometimes written as G210). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G21.0 (Secondary parkinsonism) a billable code?

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

What MS-DRG does G21.0 group to?

When malignant neuroleptic syndrome is the principal diagnosis on an inpatient stay, it groups to MS-DRG 91, 92, 93, with relative weights from 0.7783 to 1.7050 depending on complications. Higher weights mean higher Medicare reimbursement.

Is G21.0 a CC or MCC?

CMS lists G21.0 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 59 closely related codes in its exclusion list.

Can G21.0 be reported with G21.11?

Not as a rule. The Excludes1 note on G21.0 lists "neuroleptic induced parkinsonism (G21.11)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).