A few population-based studies describe the incidence of gross proteinuria in people with diabetes. We performed a population-based study in southern Wisconsin of diabetic individuals diagnosed at > or = 30 yr of age either taking insulin (n = 398) or not taking insulin (n = 441). The presence of gross proteinuria (> or = 0.3 g/L) was determined by means of a reagent strip. The incidence of proteinuria in the 4-yr interval was 17.3% (95% CI 13.6-21.0) in those taking insulin and 10.7% (95% CI 7.8-13.6) in those not taking insulin. The relative risk of developing proteinuria for those in the highest level of total pack-yr smoked compared with those who had never smoked was 2.0 (95% CI 1.2-3.3) for those taking insulin and 2.5 (95% CI 1.3-4.5) for those not taking insulin. After controlling for other risk variables, the incidence of gross proteinuria was also associated with higher GHb. These data suggest that smoking and glycemic control, both potentially modifiable factors, are significant risk factors for the development of gross proteinuria.