OBJECTIVE: To evaluate the possible benefits of the routine use of ultrasound screening in pregnancy. DESIGN: A randomized controlled trial was designed to detect a 50% difference in the incidence of induction for apparent post-term pregnancies between women who were screened with ultrasound and unscreened women. A total of 1628 pregnant women from the general population were included. Eight hundred and twenty-five were allocated to an ultrasound examination at the 18th and 32nd week of pregnancy in addition to receiving routine antenatal care. The remaining 803 women received standard antenatal care, but could only be referred for ultrasound examination on clinical indication. RESULTS: The incidence of induced labor due to apparent post-term pregnancies was approximately 70% lower in the ultrasound-screened group. Inductions from all causes were also less frequent among ultrasound-screened women. There were six perinatal deaths among the screened and seven among the controls after excluding three lethal malformations among the controls. There was no difference in Apgar score after 1 min, but the proportion with Apgar score less than 8 after 5 min was lower among the screened group (P = 0.04). The need for positive pressure ventilation for more than 1 min was lower among the screened group (P = 0.02). Birth weight was slightly higher in the screened group (39 g), but the difference was not statistically significant. Among the controls three pairs of twins remained undiagnosed until the mothers were admitted to the hospital in labor at between 36 and 38 weeks gestation. CONCLUSION: These results suggest that for women who were screened with ultrasound, obstetricians were less likely to induce labor due to apparent post-term pregnancy, than for women who were not screened. All 10 pairs of twins in the screened group were diagnosed at the routine examination. These data also suggest that perinatal morbidity might be slightly lower in the screened group.