The aim of this study was to quantify the risk of congenital heart disease in diabetic mothers referred for fetal echocardiography. Of 326 diabetic pregnancies seen over a 5-year period, ten (3.1%) resulted in a fetus with congenital heart disease. Nine (90%) of the ten cardiac lesions were identified prenatally, but one fetus had a ventricular septal defect that was overlooked antenatally. Postnatal follow-up was obtained in 312 cases (95.7%). Prenatal echocardiographic examinations were performed at 18-38 weeks of gestation (median 25 weeks) and the median gestational age at diagnosis of congenital heart disease was 22 weeks (range 19-30 weeks). Following the detection of a severe cardiac anomaly, the pregnancy was terminated in three cases. Of the seven continuing pregnancies, two resulted in spontaneous intrauterine death and two babies died within the first 6 months of life. The three survivors are clinically well, but one has required postnatal catheter intervention. Our results confirm that diabetic women are at increased risk of having a baby with congenital heart disease and detailed fetal echocardiography should therefore be offered to all diabetic women during pregnancy.