Fetal weight prediction with ultrasonic measurements of biparietal diameter (BPD) and abdominal circumference (AC) using the equation by Shepard et al. [1982] was tested prospectively in 310 fetuses. Fetuses of all weight categories were included. The error of weight prediction was in the range of +684 to -880 g. One SD of prediction error was 242 g or 8.5% of birth weight. An overestimation was seen in a fetus with a birth weight of less than 2,500 g (1 SD = 183 g or 10% of birth weight). An underestimation could be observed in a fetus with a birth weight of more than 4,000 g (1 SD = 259 g or 5.7% of birth weight). The use of a combination of BPD and AC is more accurate than the use of each of these parameters. In a fetus with a birth weight of less than 2,500 g, the equations by Thurnau et al. [1983] and Weinberger et al. [1984] are of equal clinical value. The method of Shepard et al. should be complemented with measurements of the 'cephalic index' to exclude fetuses with brachycephaly or dolichocephaly, but one should be aware that the variability of weight prediction is high (2 SD = 11.4-19.8% of birth weight).