We studied 55 cases of cerebellar atrophy identified by computerized tomography. Atrophy was determined by subjective assessment and objective measurements (superior cerebellar cistern, fourth ventricle, and brainstem). Different patterns of cerebellar atrophy were related to clinical diagnoses. A high incidence of vermal atrophy was observed in primary cerebellar degeneration and chronic alcoholism. More than half the patients with alcoholism had hemispheral atrophy. Vermal atrophy and enlargement of superior cerebellar cisterns (but not hemispheral atrophy) were associated with carcinomatous cerebellar degeneration. Atrophy caused by chronic phenytoin usage showed a specific pattern of enlargement of the cisterna magna, cerebellopontine angle, and superior cerebellar cisterns. Supratentorial atrophy was increased significantly only in the alcoholics. In general, limb ataxia, dysarthria, and nystagmus were related to hemispheral but not to vermal atrophy.