United States and European consensus views differ on the place of routine ultrasound scans during pregnancy and the validity of such scans as screening tests for fetal malformations in the general population is still under debate. Four ultrasound laboratories from Obstetric and Gynecology departments of Belgian University hospitals and affiliated hospitals have conducted a prospective study from 1984 to 1989 to compare the anomalies discovered in ultrasonic screening of the fetus with the anomalies of the neonates. Of 16,370 pregnant women at normal risk for congenital anomalies attending the antenatal clinics of these hospitals, 16,072 have had at least one ultrasound screening for congenital anomalies (98.5%). Congenital anomalies, single or multiple and 'minor' or 'major', were clearly defined in order to allow comparisons. The excluded congenital anomalies were listed as defined in the Eurocat Register. A total of 381 fetuses (2.3%) were structurally abnormal. Of the 381, 154 were correctly detected by ultrasound (sensitivity 40.4%). Altogether 15,972 fetuses were true negatives (specificity 99.9%). Eight (0.05%) were false positive for congenital anomalies. The positive predictive value was 95.1% and the negative predictive value was 98.6%. Ultrasound diagnoses were correctly achieved before 23 weeks of gestation for 21% of the anomalies. The gestational age, operator and technical dependence of ultrasound screening for congenital anomalies is discussed.