Chapter 6

G00–G99: Diseases of the Nervous System

Diseases of the Nervous System diagnostic classification updated for 2026.

Chapter Instructions

Excludes2(Not included here)
  • 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)
All CodesBillable Only
Internal Codes
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  • G11.19—

    Other early-onset cerebellar ataxia

  • G11.2—

    Late-onset cerebellar ataxia

  • G11.3—

    Cerebellar ataxia with defective DNA repair

  • G11.4—

    Hereditary spastic paraplegia

  • G11.5—

    Hypomyelination - hypogonadotropic hypogonadism - hypodontia

  • G11.6—

    Leukodystrophy with vanishing white matter disease

  • G11.8—

    Other hereditary ataxias

  • G11.9—

    Hereditary ataxia, unspecified

  • G12—

    Spinal muscular atrophy and related syndromes

  • G12.0—

    Infantile spinal muscular atrophy, type I [Werdnig-Hoffman]

  • G12.1—

    Other inherited spinal muscular atrophy

  • G12.2—

    Motor neuron disease

  • G12.20—

    Motor neuron disease, unspecified

  • G12.21—

    Amyotrophic lateral sclerosis

  • G12.22—

    Progressive bulbar palsy

  • G12.23—

    Primary lateral sclerosis

  • G12.24—

    Familial motor neuron disease

  • G12.25—

    Progressive spinal muscle atrophy

  • G12.29—

    Other motor neuron disease

  • G12.8—

    Other spinal muscular atrophies and related syndromes

  • G12.9—

    Spinal muscular atrophy, unspecified

  • G13—

    Systemic atrophies primarily affecting central nervous system in diseases classified elsewhere

  • G13.0—

    Paraneoplastic neuromyopathy and neuropathy

  • G13.1—

    Other systemic atrophy primarily affecting central nervous system in neoplastic disease

  • G13.2—

    Systemic atrophy primarily affecting the central nervous system in myxedema

  • G13.8—

    Systemic atrophy primarily affecting central nervous system in other diseases classified elsewhere

  • G14—

    Postpolio syndrome

  • G20—

    Parkinson's disease

  • G20.A—

    Parkinson's disease without dyskinesia

  • G20.A1—

    Parkinson's disease without dyskinesia, without mention of fluctuations

  • G20.A2—

    Parkinson's disease without dyskinesia, with fluctuations

  • G20.B—

    Parkinson's disease with dyskinesia

  • G20.B1—

    Parkinson's disease with dyskinesia, without mention of fluctuations

  • G20.B2—

    Parkinson's disease with dyskinesia, with fluctuations

  • G20.C—

    Parkinsonism, unspecified

  • G21—

    Secondary parkinsonism

  • G21.0—

    Malignant neuroleptic syndrome

  • G21.1—

    Other drug-induced secondary parkinsonism

  • G21.11—

    Neuroleptic induced parkinsonism

  • G21.19—

    Other drug induced secondary parkinsonism

  • G21.2—

    Secondary parkinsonism due to other external agents

  • G21.3—

    Postencephalitic parkinsonism

  • G21.4—

    Vascular parkinsonism

  • G21.8—

    Other secondary parkinsonism

  • G21.9—

    Secondary parkinsonism, unspecified

  • G23—

    Other degenerative diseases of basal ganglia

  • G23.0—

    Hallervorden-Spatz disease

  • G23.1—

    Progressive supranuclear ophthalmoplegia [Steele-Richardson-Olszewski]

  • G23.2—

    Striatonigral degeneration

  • G23.3—

    Hypomyelination with atrophy of the basal ganglia and cerebellum

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