'Arteriosclerotic' parkinsonism is still a subject of debate. The aim of this study was to investigate whether parkinsonism associated with basal ganglia lacunes possesses peculiar clinical features and a clinical course which enables its distinction from idiopathic Parkinson's disease (IPD). 106 consecutive ambulatory patients with the clinical diagnosis of parkinsonism were referred for CT examination. Patients in whom isolated basal ganglia lacunes were found were interviewed and examined, and their clinical characteristics were compared to those of patients suffering from IPD without lacunes (controls). In 20 patients, isolated basal ganglia lacunes were detected; all had risk factors for stroke (significantly more than controls) and 7 of them had had clinically diagnosed strokes. The extrapyramidal disability evolved slowly in all. The clinical picture was indistinguishable from IPD in individual patients. However, tremor was significantly less frequent in this group. Lower body parkinsonism was not observed. Extra-pyramidal signs were frequently asymmetrical (55%), with no consistent relationship to the side of the lacune. Asymmetrical pyramidal signs were present in 30% of those with unilateral lacunes, always on the appropriate side. Only 1 patient was an L-dopa nonresponder. Patients with parkinsonism associated with basal ganglia lacunes showed tremor less frequently than other IPD patients; otherwise, clinical features and course of the disease were indistinguishable from IPD. In these cases, parkinsonism and basal ganglia lacunes might have occurred independently of each other and tremor might have been prevented by ischemic events.