The validity of the Stage II ultrasound examination for fetal congenital anomalies has been determined. Only pregnancies that fulfilled certain criteria, i.e. obstetric complications (IUGR, polyhydramnios, immature-premature uterus contractions), or women with a history of congenital anomalies qualified. Five hundred and fifteen pregnant women were examined. Follow-up evaluation was available on 481 pregnancies (494 neonates). Of these children 102 (21%) appeared to have one or more structural anomaly following birth. In 88 of them at least one congenital anomaly had been detected antenatally by the Stage II ultrasound examination. The sensitivity of the ultrasound scanning procedure was 86%, the specificity 100%. The validity of the applied selection criteria for the Stage II ultrasound examination was studied in 2059 women who had delivered consecutively in our hospital. One hundred and eighty-one had the Stage II ultrasound examination performed. Thirty-six of these 181 women delivered an infant with a structural anomaly (20.0%). The remaining 1878 did not qualify for the Stage II ultrasound examination. From these pregnancies 24 infants were born with a structural anomaly (1.3%). The sensitivity of the applied selection criteria was 60% and the specificity 93%. The incidence of congenital anomalies was strikingly higher in pregnancies scanned for reasons of obstetric complications than in the pregnancies scanned for a history of congenital anomalies. The necessity of the Stage II ultrasound examination in every pregnancy is questioned on the basis of the results.