Thirty-two patients with primary progressive cerebellar ataxia were studied using MRI. This technique is better than CT in demonstrating atrophy of cerebellar structures as well as of brainstem and spinal cord. The differential diagnosis from other diseases particularly with multiple sclerosis is easier. The degree of ataxia correlated well with the degree of atrophy of cerebellum. However we could not see any correlation between the degree of atrophy and the onset and duration of the disease and no certain specific aspects could be demonstrated in the different groups examined.