Antenatal erect lateral X-ray pelvimetry was performed for 116 primigravidas and 53 multigravidas because of suspected cephalopelvic disproportion (CPD). Multigravidas were further subgrouped into 4 gravidas and greater than 4 gravidas. In the primigravidas, there was no statistical difference in the mean value of the anteroposterior diameter of the pelvic inlet (APD) of the elective (10.4 cm, +/- 0.6 SD) and the emergency (10.5 cm, +/- 0.9 SD) caesarean section group. In the multigravidas, the mean value of the APD showed a statistically significant decrease with increased parity. In this group, the chances of delivery by caesarean section were 74%, when the APD was less than 10.5 cm, and 12% if the APD was greater than 11.5 cm. It is concluded that cephalopelvic disproportion in primigravidas should only be diagnosed after adequate trial of labour with adequate uterine contractions. In multiparous patients, especially grand multiparas, X-ray pelvimetry is recommended in cases of suspected CPD before a trial of vaginal delivery is conducted, since the mode of delivery seems to depend primarily on the pelvic capacity.