From 1 January 1985 to 31 December 1990, the Northern Region Fetal Abnormality Survey received 736 notifications of fetuses with suspected urological abnormalities; a prevalence of three per 1000 births. There was a male:female ratio of 2:1, the ratio was higher in obstructive than in intrinsic renal parenchymal lesions. Overall diagnostic sensitivity was 68.9% and positive predictive value 50.8%. Hydronephrosis was the most frequent antenatal diagnosis (421 cases, 57.2%): 233 (55.3%) of these were found to be normal postnatally. There were 52 other false positive diagnoses. Of 113 babies with confirmed hydronephrosis antenatal diagnosis was correct in 97, sensitivity 85.8%, specificity 48.1%; 1.8% of these had chromosome defects. In 33 cases of bilateral renal agenesis antenatal diagnosis was correct or potentially correct in 24, sensitivity 72.7%, specificity 98.9%. Only six of 26 babies with posterior urethral valves were suspected, sensitivity 23%, specificity 98.7%. Mortality rate in 91 babies with unsuspected abnormalities was 39.6%: overall mortality was 24.2%. Unsuspected abnormalities occurred more frequently when mothers were not scanned after the 16th week of pregnancy.