This study evaluates whether medical therapy alone can achieve satisfactory results in the treatment of low grade carotid stenosis or ulcerated plaques. Out of 525 patients presenting with transient or minor strokes, 64 were found with unilateral extracranial vascular disease as the sole potential source for their neurological symptoms. Utilizing arteriographic criteria, 35 patients with ulcerated plaques or carotid artery stenosis of less than 50% luminal artery diameter were treated conservatively with aspirin and dipyridamole (300 mg/day each). Twenty-nine patients with unilateral internal carotid artery stenosis of greater than 50% luminal artery diameter were treated by means of carotid endarterectomy. Follow-up in the two groups for a mean period of 24-26 months revealed no major strokes or neurological deaths in either group. Myocardial infarction was the major cause of death. Two patients developed subsequent transient ischemic attacks, and one a minor stroke with total recovery in the conservatively treated group. All became asymptomatic when warfarin replaced aspirin therapy. The findings in this study confirmed that "low grade" stenoses can be safely treated by medical measures alone.