The results of erect lateral X-ray pelvimetry in a retrospective study of 100 randomly selected patients who had undergone previous caesarean section for a variety of indications were analysed. The indication for caesarean section was compared with subsequent pregnancy outcome. The inlet diameter and sacral shape were not found to be of great predictive value. Radiological engagement of the fetal head was associated with a 90% incidence of vaginal delivery.