Cranial computer tomographic (CT) images of 33 patients with multiple system atrophy (MSA) and of 40 age-matched controls were blindly analyzed by two neuroradiologists. All patients had autonomic dysfunction, all but one had parkinsonism, and 13 had cerebellar signs. The scans were judged entirely normal in 21%. Moderate or severe infratentorial atrophy was found in 42%. Cerebellar atrophy was present in 39%, and pontine atrophy was present in 18%. Of the 13 patients with cerebellar signs, only eight had cerebellar atrophy. Of the 20 patients without cerebellar signs, five had cerebellar atrophy. Supratentorial involvement was much less common and less severe. Thus, CT demonstrated system involvement that was not evident clinically in five of 33 cases (15%). However, in all five the clinical diagnosis was already evident from the presence of both autonomic and pyramidal signs in addition to parkinsonism. We conclude that CT imaging is of limited diagnostic use in individual patients with MSA.