2027 ICD-10-CM Diagnosis Code G20.CParkinsonism, unspecified

ICD-10-CM Codes›G00–G99›G20-G26›G20

ICD-10-CM G20.C
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G20.C is a billable ICD-10-CM diagnosis code for parkinsonism, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 56 through 57. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Parkinson's disease.

For Medicare Advantage risk adjustment, G20.C maps to CMS-HCC Category 199 (Parkinson and Other Degenerative Disease of Basal Ganglia) under the V28 model, adding a risk factor of about 0.615 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
G20.C
Billable Status
Yes — Valid for Submission
Code Describes
Parkinsonism, unspecified
Short Description
Parkinsonism, unspecified
Same as the full description in the CMS dataset.
Parent Code
G20
Parkinson's disease

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG20-G26Extrapyramidal and movement disorders
CategoryG20Parkinson's disease
This CodeG20.CParkinsonism, unspecified

Medicare Risk Adjustment (HCC)Billing

G20.C maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 199— Parkinson and Other Degenerative Disease of Basal Ganglia
Payment HCC · PY 2027 one of 16 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.615
community, non-dual, aged · ranges 0.219–0.634 across segments
Hierarchy
Top of its hierarchy
HCC 199 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 78
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 78 · ESRD (V21): HCC 78 · ESRD (V24): HCC 78
ESRD V21 weights: 0.065 dialysis, 0.141–0.583 functioning graft · ESRD V24 weights: 0.079 dialysis, 0.206–0.608 functioning graft
Part D (RxHCC)
RxHCC 161 — Parkinson Disease
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adult-onset dystonia parkinsonism
  • Amyotrophic lateral sclerosis with dementia
  • Amyotrophic lateral sclerosis with parkinsonism
  • Amyotrophic lateral sclerosis, parkinsonism, dementia complex
  • Amyotrophic lateral sclerosis, parkinsonism, dementia complex of Kii Peninsula
  • Amyotrophic lateral sclerosis, parkinsonism, dementia complex of West New Guinea
  • Atypical juvenile parkinsonism
  • Atypical Parkinsonism
  • Developmental delay, language impairment, dopa responsive dystonia, parkinsonism syndrome
  • Dissociative neurological symptom disorder co-occurrent with parkinsonism
  • Dopamine transporter deficiency syndrome
  • Early onset parkinsonism and intellectual disability syndrome
  • Frontotemporal dementia with parkinsonism-17
  • Functional parkinsonism
  • Hemiparkinsonism hemiatrophy syndrome
  • Hypokinetic parkinsonian dysphonia
  • Parkinsonian facies
  • Parkinsonian pyramidal syndrome
  • Parkinsonian tremor
  • Parkinsonism
  • Parkinsonism due to heredodegenerative disorder
  • Parkinsonism with polyneuropathy
  • Parkinson's disease
  • Perry syndrome
  • Rapid onset dystonia parkinsonism
  • Symptomatic parkinsonism
  • X-linked dystonia parkinsonism
  • X-linked parkinsonism with spasticity syndrome
  • Young onset Parkinson disease

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G20.C: its own notes plus those printed at G20 and Chapter 6. A note printed at a category, block or chapter applies to every code under it.

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.

  • Parkinsonism, NOS

Excludes1

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

  • Parkinson's disease NOS (G20.A1)
  • Parkinson's disease with dyskinesia (G20.B-)
  • Parkinson's disease without dyskinesia (G20.A-)
  • secondary parkinsonism (G21.-)

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.

From G20 Parkinson's disease applies to 5 codes

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name G20.C, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming G20.C: they are not reported together with it, unless the two conditions are unrelated.

  • 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 G20.C: 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

Code First 3

These codes say to code first a condition named in the note, and G20.C is one of the conditions named.

  • F02 Dementia in other diseases classified elsewhere
    Parkinson's disease (G20.-) names G20.-, which includes this code
  • F06.7 Mild neurocognitive disorder due to known physiological condition
    Parkinson's disease (G20.-) names G20.-, which includes this code
  • R47.82 Fluency disorder in conditions classified elsewhere
    Parkinson's disease (G20.-) names G20.-, 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 NVS004
Parkinson's disease
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Parkinsonian Disorders

    a group of disorders which feature impaired motor control characterized by bradykinesia, muscle rigidity; tremor; and postural instability. parkinsonian diseases are generally divided into primary parkinsonism (see parkinson disease), secondary parkinsonism (see parkinson disease, secondary) and inherited forms. these conditions are associated with dysfunction of dopaminergic or closely related motor integration neuronal pathways in the basal ganglia.

Patient EducationClinical

Parkinson's Disease

Parkinson's disease (PD) is a type of movement disorder. It happens when nerve cells in the brain don't produce enough of a brain chemical called dopamine. Sometimes it is genetic, but most cases do not seem to run in families. Exposure to chemicals in the environment might play a role.

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement G20.C replaces the following previously assigned code(s):

  • G20 - Parkinson's disease
FY 2024AddedAdded to the ICD-10-CM code setEffective October 1, 2023.
FY 2025–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G20.COverview

What is the ICD-10 code for parkinsonism, unspecified?

The ICD-10-CM code for parkinsonism, unspecified is G20.C (sometimes written as G20C). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G20.C (Parkinson's disease) a billable code?

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

What MS-DRG does G20.C group to?

When parkinsonism, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 57, 56, with relative weights from 1.2835 to 2.2649 depending on complications. Higher weights mean higher Medicare reimbursement.

Can G20.C be reported with G20.A1?

Not as a rule. The Excludes1 note on G20.C lists "Parkinson's disease NOS (G20.A1)". 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).

Does G20.C need an additional code?

When the condition applies, yes. The Use Additional Code note at G20, which applies to G20.C, reads: code, if applicable, to identify: dementia with anxiety (F02.84, F02.A4, F02.B4, F02.C4); dementia with behavioral disturbance (F02.81-, F02.A1-, F02.B1-, F02.C1-); dementia with mood disturbance (F02.83, F02.A3, F02.B3, F02.C3); dementia with psychotic disturbance (F02.82, F02.A2, F02.B2, F02.C2); dementia without behavioral disturbance (F02.80, F02.A0, F02.B0, F02.C0); and 1 more listed in the Instructional Notes section. The additional code is reported after G20.C.

What HCC is G20.C?

G20.C (parkinsonism, unspecified) maps to CMS-HCC Category 199 (Parkinson and Other Degenerative Disease of Basal Ganglia), commonly written as HCC 199, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 78 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 161.

Does G20.C risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G20.C adds a risk adjustment factor of about 0.615 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.219 to 0.634 depending on the payment segment). HCC 199 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 199 category page.