A scoring system has previously been developed to diagnose intrauterine growth retardation (IUGR) based on three parameters: estimated fetal weight, amniotic fluid volume, and maternal blood pressure status. To test the IUGR score prospectively, the authors computed the score in 356 third-trimester fetuses, 39 growth retarded and 317 normal, scanned within 2 weeks prior to delivery. The IUGR score identified three groups, each with a distinct probability of IUGR: A score below 50 virtually excludes IUGR (3% probability), a score above 60 allows confident diagnosis (74% probability), and score of 50-60 is indeterminate (13% probability). The IUGR score performed best in patients with accurate dating by early ultrasound (US), but even among patients lacking accurate dating, the performance of the IUGR score was superior to that previously reported for any single sonographic parameter. The IUGR score can be used in any US facility to diagnose or exclude third-trimester IUGR.