The incidence of retinopathy was assessed in 188 diabetic and 284 nondiabetic Pima Indian adults six years after an initial examination had shown each to be free of retinopathy. Exminations included direct ophthalmoscopy through dilated pupils. The incidence of retinal lesions was strongly related to the presence of diabetes and, among the diabetic subjects, to insulin treatment, disease duration, plasma glucose concentration, and presence of other complications such as proteinuria, loss of deep tendon reflexes, and increased vibration-sensation threshold. In diabetic subjects not taking insulin, the incidence of exudates in those with systolic blood pressures of at least 145 mm Hg was more than twice that of those with pressures of less than 125 mm Hg. This association persisted when assessed within categories of subjects stratified according to 13 potentially confounding variables, suggesting that control of blood pressure may reduce the incidence of retinal exudates in diabetics not treated with insulin.