We describe the computerized tomography findings in 85 patients affected with degenerative ataxias. Cerebellar atrophy was moderate in patients with Friedreich's disease (no. 28) and early onset cerebellar ataxia with retained reflexes (no. 10) and, in Friedreich's disease, it was mostly a late feature. On the contrary, in symptomatic patients with adult onset dominant cerebellar ataxia (no. 24), cerebellar atrophy was always present and often marked. However, it was absent in 3 asymptomatic affected relatives. Infratentorial and supratentorial atrophy were frequent findings in idiopathic late onset cerebellar ataxia (no. 16).