We prospectively studied the results of carotid angiography in 45 patients with transient or nondisabling neurologic deficits caused by lacunar infarction in the internal capsule or corona radiata and demonstrated by computed tomography. An ipsilateral stenosis at the bifurcation of the internal carotid artery was found in 14 patients (31%, 95% confidence limits 18-47%), seven of whom also had stenosis of the contralateral internal carotid artery. In previous studies an average of 65% of patients with transient hemispheric deficit had internal carotid artery stenosis or occlusion. Hypertension and hypertensive retinal vasculopathy assessed by fundus photographs were found in most patients, but not significantly more often in the patients without internal carotid artery stenosis. Our findings support the notion that small vessel disease rather than emboli from the carotid bifurcation is the most common cause of lacunar infarction.