A family with two members who had early-onset cerebellar ataxia (EOCA) with retained tendon reflexes had, in addition to their motor deficits, a progressive impairment of cognitive and visuospatial abilities. We used positron emission tomography (PET) with 11C-flumazenil to study gamma-aminobutyric type A/benzodiazepine receptor binding (BZR) and 18F-2-fluoro-2-deoxy-D-glucose to analyze longitudinally regional cerebral glucose metabolism. Flumazenil-PET demonstrated loss of BZR binding that has not been shown in Friedreich's ataxia and olivopontocerebellar atrophy. These findings may be useful for differentiation of EOCA from other types of cerebellar ataxia. In comparison to age-matched control subjects, these patients showed a global metabolic decline and predominant hypometabolism in the thalamus and cerebellum. The progressive metabolic derangement may be explainable by a disturbed integrity of cognition-related networks resulting from secondary degeneration of cerebello-thalamo-cortical projections.