Young African and Indian patients (age of onset under 35) were studied in order to determine the pattern of diabetes mellitus seen in these groups. Of the 110 African patients 86 had IDDM and 18 NIDDM, whereas of the 101 Indian patients the distribution was 40 and 60 respectively. Tropical diabetes (J-type and Z-type) was rare in both groups. IDDM tended to start at an earlier age in Indians (mean 17 years) compared to Africans (mean 23 years). Onset of the disease tended to be more frequent in winter, particularly in Indian patients. NIDDM was associated with a female predominance (3:1) and obesity in both population groups. A positive family history of diabetes mellitus was obtained from 80% of the Indian and 39% of the African patients with NIDDM.