The incidence of TIA, stroke, and neuropathy was studied in a community-based maturity-onset diabetic population. The frequencies of TIA and stroke were increased in maturity-onset diabetic patients as compared to the population of Rochester, Minnesota. The median age of occurrence of TIA and stroke in diabetics was 74 years, not significantly different from that in non-diabetics. Diabetic patients with hypertension at the time of diagnosis of diabetes mellitus had an increased frequency of TIA and stroke. Control of hypertension and/or diabetes mellitus was associated with a decreased frequency of TIA or stroke. Obesity, clinical coronary heart disease, and an abnormal electrocardiogram at the time of diagnosis of diabetes mellitus were not associated with a significantly increased frequency of TIA or stroke. The most common type of peripheral neuropathy in diabetes mellitus was distal polyneuropathy. Mononeuropathy and autonomic neuropathy were much less frequent. The frequency of distal polyneuropathy increased with the duration of diabetes mellitus. The frequency of neuropathy was increased in patients with poor control, reemphasizing the importance of diabetic control in the prevention of diabetic complications.