Blacks and Indians with early-onset insulin-dependent diabetes mellitus (IDDM) were studied in order to assess the prevalence of acute and chronic complications. Of the 92 Blacks almost 70% developed ketoacidotic coma on one or more occasions, whereas 50% of the 41 Indians manifested this complication. Most of the chronic complications were related to duration of IDDM. Retinopathy was found in 14% of the Black and 22% of the Indian patients, nephropathy in 3% and 7% and neuropathy in 22% and 32% respectively. Compared with findings in other studies, IDDM in these population groups is not associated with a particularly high prevalence of chronic complications.