Diabetic pregnancies complicated by preeclampsia are of concern because of poor perinatal outcome. However, with improved maternal and fetal surveillance the impact of preeclampsia in diabetic pregnancies is declining. This prospective controlled study compared the incidence of preeclampsia and maternal-fetal outcome in 334 diabetic pregnancies and 16,534 nondiabetic pregnancies. The incidence of preeclampsia was 9.9% (33/334) in diabetic pregnancies compared with 4.3% (716/16,534) in nondiabetic controls. The incidence of preeclampsia rose with increasing severity of diabetes by White classification, but was still 8.9% after exclusion of diabetic patients with nephropathy or chronic hypertension. The perinatal mortality rate per 1000 births was 60 for preeclamptic diabetic patients compared with 3.3 for normotensive diabetic patients. Parity, maternal age, and blood glucose control were similar in preeclamptic diabetic patients compared with normotensive diabetic patients. We conclude that preeclampsia is twice as common in diabetic pregnancies compared with normal controls.