In spite of the widespread use of ultrasonographic estimates of fetal weight, a paucity of data exists with regard to its use in patients who are in labor. The purpose of this study was to evaluate the accuracy of ultrasonographic estimates of fetal weight in a busy labor and delivery suite by the house staff. Measurements of biparietal diameter, abdominal circumference, and femur length were prospectively obtained in 109 patients in labor in whom this information was expected to be contributory in making delivery plans. All patients were delivered within 48 hours of ultrasonographic evaluation. Measurements of abdominal circumference were obtained in all cases, Biparietal diameter and femur length were obtained in 85% and 92% of cases, respectively. Overall, the mean absolute errors were 9.3% and 9.2% for estimated fetal weight by biparietal diameter/abdominal circumference and abdominal circumference/femur length ratios, respectively. Estimated fetal weight by biparietal diameter/abdominal circumference ratio was not significantly different from that by femur length/abdominal circumference ratio. In conclusion, the accuracy of intrapartum estimates of fetal weight performed by the house staff in a busy labor and delivery unit is comparable to that reported for estimates obtained during the antepartum period by professional users of ultrasonography in a controlled setting.