To determine whether MRI can reveal more vascular lesions in patients clinically suspected of having vascular parkinsonism, we compared 15 such patients with 15 patients who had idiopathic Parkinson's disease and 10 hypertensive controls. Patients with suspected vascular parkinsonism had significantly more subcortical lesions than those with Parkinson's disease or hypertension. The cutoff point that best distinguished patients with suspected vascular parkinsonism from patients with Parkinson's disease was a 0.6% level of lesioned brain tissue volume. There were two types of vascular parkinsonism: one had an acute onset and lesions located in the subcortical gray nuclei (striatum, globus pallidus, thalamus); the other had an insidious onset and lesions diffusely distributed in the watershed areas.