The prevalence of macro- and microvascular disease and the distribution of glycosylated hemoglobin (Hb A1) were assessed in a representative Danish diabetes population living on the island of Falster with a population of 44.498 inhabitants. The diabetes population consisted of 533 diabetics of whom 166 were insulin-dependent (type I) and 367 non-insulin-dependent (type II). Among the 533 diabetics macrovascular complications as evidenced by myocardial infarction, gangrene or amputations and cerebrovascular catastrophes were present in 8%, 5% and 7%, respectively, while microvascular disease as evidenced by diabetic retinopathy was present in 53% of the cases. Multilogistic analysis showed no relationship between the macrovascular complications and the level of Hb A1, whereas there was a highly significant correlation between the level of Hb A1 and the presence of retinopathy in both patients with type I (P less than 0.01) and type II diabetes (P less than 0.001). The results emphasize the contention that the development of microvascular disease depends on the quality of blood glucose control while that of macrovascular disease seems unrelated to long-term hyperglycemia.