Perinatal morbidity and mortality are still high in cases of intra-uterine growth retardation. Present screening methods select large risk groups and have a low positive predictive value. Instruments which could be used as indicators for those cases within the risk group needing close fetal monitoring would be valuable. The aim of this prospective study was to evaluate fetal ponderal index with respect to signs of fetal distress and neonatal outcome. By means of a risk scoring system, 73 pregnancies with increased risks of intra-uterine growth retardation were compared with 61 controls. By means of ultrasound, fetal weight was estimated and the fetal femur measured. The fetal ponderal index was calculated by dividing the estimated fetal weight in grams by the third power of the femur length. In the control group, 5/61 showed signs of distress and in the risk group, 43/73. The mean fetal ponderal index of the controls was 8.60 (SD 0.84) and in the risk group 7.72. The groups were compared with each other with respect to signs of distress. The fetuses showing signs of distress had a mean FePI of 7.45 (p less than 0.001). Those (30/73) in the risk group not showing signs of fetal distress had a mean value of 8.14 and differed significantly (p less than 0.001) from the distress group. Fetal ponderal index would seem to be a valuable adjunct for the differentiation of the more susceptible fetuses in an intra-uterine growth retardation risk group.