In a population-based study in southern Wisconsin, 1370 diabetic persons diagnosed after 29 years of age were examined using standard protocols to determine the prevalence of proteinuria and associated risk variables. Proteinuria (greater than or equal to 0.30 g/L) was present in 18.0% of persons taking insulin and 12.2% of the persons not taking insulin. Proliferative retinopathy and proteinuria were associated with each other. Proteinuria was also associated with increasing duration of diabetes, high systolic blood pressure, use of digoxin, and being male, but not with a history of cigarette smoking or metabolic control as measured by glycosylated hemoglobin.