Probable or possible multiple system atrophy (MSA) was diagnosed on strict clinical criteria in 42 patients: 20 with combined parkinsonism and cerebellar ataxia, 9 with striatonigral degeneration (SND) and 13 with olivopontocerebellar atrophy (OPCA). All patients were then studied with 0.5 and/or 1.5 Tesla magnetic resonance (MR) units. MR imaged putaminal abnormalities in all 9 patients with SND and posterior fossa abnormalities consistent with OPCA in all 13 patients with this diagnosis. Of the 20 patients with parkinsonism and cerebellar involvement, classified as probable MSA, 7 presented putaminal abnormalities only, 3 abnormalities consistent with OPCA only and 10 a combination of both. These findings show strong MRI support for the clinical diagnosis of MSA.