AIM: To clarify the usefulness of the fetal-pelvic index as a predictor of vaginal birth after previous lower segment cesarean section. METHODS: One hundred and seventy women with one lower segment cesarean section who attempted for trial of vaginal birth were enrolled. Pelvimetry was performed to measure maternal pelvic inlet and mid-cavity circumferences at 37 weeks gestation. Ultrasound was performed to measure fetal head and abdominal circumferences at 38-39 weeks. The fetal-pelvic index was derived. The predictability of fetal-pelvic index in the predicting the outcome of delivery was calculated. RESULTS: Fifty-seven (33.5%) women required repeated cesarean section and 113 (66.5%) delivered vaginally. Twenty-two women with positive fetal-pelvic index had repeated cesarean section. The predictability of positive fetal-pelvic index was 48.9%. Ninety of the 125 patients with a negative fetal-pelvic index delivered vaginally. The predictability of negative fetal-pelvic index was 72.0%. CONCLUSIONS: Fetal-pelvic index derived in the antenatal period has low predictive value in predicting of successful vaginal birth after cesarean section. This index is not useful in clinical practice.