Standard ultrasound measurements were performed by two observers in 40 third-trimester fetuses. Observers were blinded to the results of the meaurements. Estimated fetal weight (EFW) was calculated using two published formulae. The intra-observer standard deviation for EFW, assessed using one-way analysis of variance, was <75 g for both observers. The 95% prediction intervals for inter-observer comparisons of EFW, calculated using the limits of agreement method, were − 187.3 g to 139.8 g, and − 159.9 g to 124.3 g, using the two formulae. The results suggest that measurements of EFW are reproducible. The prediction interval is comparable to the weekly fetal weight increment in normal fetuses. © 1993 John Wiley & Sons, Inc.