It is commonly assumed that in patients the risks of developing nephropathy and uraemia are high in type I and low in type II diabetes mellitus. Since type II occurs mostly in elderly individuals with limited life expectancy and high cardiovascular mortality, the true risk may have been underestimated, as many patients do not survive to experience renal complications. To assess renal risk further, we evaluated all patients with type II and type I diabetes mellitus without severe secondary disease who were followed in the outpatient clinic between 1970 and 1985. The cumulative risk of proteinuria after 20 years of diabetes mellitus was 27% in type II and 28% in type I, the findings after 25 years were 57% and 46% respectively. The cumulative risk of renal failure, i.e. serum creatinine greater than 1.4 mg/dl, after 3 years of persisting proteinuria was 41% in both type II and type I, and after 5 years of proteinuria were 63% and 59% respectively. We conclude that the renal risk is similar in patients with type II and type I diabetes mellitus.