Our objectives were to determine the accuracy of antenatal sonography for the detection of congenital renal malformations and to characterize the type of malformations, seen in a 3-year prospective study at a university-affiliated maternity hospital. Participants were 31,217 pregnant women, during the study period, and subjects were 65 fetuses in whom renal malformations were detected on antenatal ultrasound. Pelvic ultrasound scans were performed at least once between 20 and 37 weeks' gestation on all pregnant women attending the antenatal clinic of the hospital for the detection of renal malformations. Fetal urinary sampling, diversion procedures, or termination of pregnancy were carried out as required in those detected to have renal anomalies. Postnatal diagnosis was confirmed by sonography or autopsy. Diagnostic procedures and renal surgery were performed postnatally if indicated. Sixty-five fetuses (0.2 per cent) were diagnosed to have congenital renal malformation antenatally at a mean gestational age of 28.4 weeks. A dilated urinary system was seen in 39, cystic renal disease in 15, agenesis/hypoplasia in six, combined lesions in four, and a horseshoe kidney in one. Oligohydramnios was noted in 20 (31 per cent) pregnancies. Multiple congenital malformations associated with renal anomalies were detected in 12 pregnancies. Termination was carried out at 20 weeks in two pregnancies for lethal malformations; fetal urinary sampling was done in two fetuses with obstructed uropathy, and a vesicoamniotic shunt inserted in one. Postnatal ultrasound confirmed a dilated urinary system in 32, cystic renal dysplasia in 15, renal aplasia/hypoplasia in five, combined lesions in six, and a horseshoe and an ectopic kidney in one each. Five infants were found to be normal. There were seven stillbirths and seven neonatal deaths. Radionuclide scans showed obstruction in nine, decreased renal function in six, and absent renal functions in 10 infants. Micturating cystourethrography demonstrated reflux in 11 and a non-refluxing non-obstructive dilated renal system in five babies. Renal surgery was performed in nine infants. The conclusions drawn from this study were that antenatal detection of renal disease is fairly accurate, even in an extremely busy hospital and certain types of malformations reported in other studies were not observed, despite a large cohort.