Since cephalopelvic disproportion inevitably leads to cesarean section it seems to be mandatory to identify patients with an absolute discrepancy between the size of the fetus and the birth canal in order to avoid unnecessary trials of labour. In a case control study, comparing a group of patients who delivered by cesarean section because of cephalopelvic disproportion with an age matched control group, routinely assessed pelvic measurements and measurements of the newborn were correlated to cephalopelvic disproportion. Multivariate linear regression was applied to each group to determine, which of the maternal and fetal factors had the strongest influence on the mode of delivery. In the study group external conjugate showed the strongest positive relation to maternal body height (P < 0.01), the biparietal diameter of the newborn was negatively correlated (P < 0.01). None of the analyzed variables reached statistical significance in the control group. Differences between the two groups were marginal, thus providing no safe basis for decision making even in a population at high risk for developing cephalopelvic disproportion.