This study prospectively examined the use of umbilical artery flow velocimetry for monitoring fetal health in postdate pregnancies. Forty-six patients with well-established dates were evaluated with semiweekly biophysical profiles and umbilical artery flow velocimetry (characterized by the ratio of the peak systolic to end-diastolic velocity). Their labor records were reviewed, and neonates were examined for signs of postmaturity. Twenty neonates had an abnormal test result or outcome (identified as an abnormal nonstress test, oligohydramnios, meconium, intrapartum fetal distress, or a 5-minute Apgar score less than 7). Nine neonates had a physical examination consistent with the postmaturity syndrome. Twenty-one neonates were entirely normal. Comparisons of the mean systolic/diastolic ratios for neonates with and without the complications associated with postdatism showed no significant differences. In addition, all systolic/diastolic ratios were within the normal range. Therefore, umbilical artery flow velocimetry is unlikely to be useful for the routine antenatal assessment of the postdate fetus.