A one-stage ultrasound screening program was evaluated, using a pregnancy/perinatal database containing information from 2766 pregnancies and deliveries. Among women who did not have a second-trimester ultrasound examination, labor was induced for presumed post-term pregnancy in 4.0% versus 1.6% of pregnancies in the screening group (p = 0.007). In the group with second-trimester ultrasound scanning other than screening, the frequency was 3.2%. Of women with spontaneous labor or who were induced for presumed post-term pregnancy, 3.8% in a screening group and 8.0% in a group with other second-trimester ultrasound examination were post-term according to BPD measurements (p = 0.0003). In the screening group, 6.2% of liveborn singletons were small for gestational age (less than the 10th percentile) compared with 8.5% in the non-screening group (p less than 0.05). A subset of 365 screened women with optimal menstrual history had spontaneous labor or were induced for presumed post-term pregnancy. According to menstrual history and ultrasound examination, 7.4% and 3.8% of these were post-term, respectively (p = 0.04). It is concluded that the main value of screening lies in a more accurate dating of pregnancy, even when menstrual history is optimal, with a lower incidence of induced labor for believed post-term pregnancies. In addition, there may be an improvement in the obstetric management of pregnancy, reflected in our study as a lower incidence of small for gestational age infants.