The relation between diabetic microangiopathy and macroangiopathy was studied by analysing the relative mortality from cardiovascular disease in patients with insulin dependent diabetes mellitus with and without persistent proteinuria. The study group comprised 2890 diabetics diagnosed between 1933 and 1972 before the age of 31, and the study was conducted by using the linear logistic discrete failure time model. In patients with proteinuria the relative mortality from cardiovascular disease was 37 times that in the general population; in patients without proteinuria it was 4•2 times that in the general population. In both groups women had a relative mortality twice to 2•6 times that of men. In neither group was relative mortality correlated with duration of diabetes, suggesting that the association between diabetes and cardiovascular disease may be conferred by factors other than hyperglycaemia and hyperinsulinaemia. The high relative mortality from cardiovascular disease in diabetics with proteinuria indicates a strong association between diabetic microangiopathy and macroangiopathy, suggesting a common (pathogenetic?) mechanism for these two late diabetic complications.