This study evaluates the wall thickness of common carotid arteries and the atherosclerotic involvement of the carotid bifurcations in patients with noninsulin-dependent diabetes mellitus (NIDDM), with and without microvascular complications. Seventy subjects affected by NIDDM, and 17 healthy controls were evaluated by means of high-resolution echo-Doppler scan. Twenty-six diabetics (Group A) and complications (overnight proteinuria > 500 mg, background retinopathy, sensory neuropathy), while 44 (Group B) had no complications. The two groups were comparable for age, sex, plasma lipid profile, and smoking habit. Arterial hypertension was present in 15 of 26 (58%) complicated patients (Group A) and in 18 of 44 (41%) uncomplicated patients (Group B). None of the patients had a history of cerebrovascular disease. The authors found that the wall thickness of the common carotid artery was greater and atherosclerotic lesions of the carotid bifurcation were more frequent in diabetic patients with microvascular complications than in uncomplicated diabetics (who had a similar distribution of other risk factors for atherosclerosis) and in nondiabetic controls. These data on the one hand confirm the role of diabetes as an independent risk factor for carotid atherosclerosis and, on the other hand, indicate a correlation between microvascular lesions and early atherosclerosis in diabetes.