The purpose of this prospective investigation was to evaluate the outcome of trial of labor in women with a history of a single low transverse cesarean section for dystocia in comparison with the outcome in women with a history of cesarean delivery for a reason other than dystocia. During the study period, 89 of 131 patients (68%) with a history of dystocia had a successful trial of labor, compared with 78 of 96 women (81%) who had cesarean delivery for a reason other than dystocia (P less than .025). Within the former group, 79% of women who originally had surgery while still in the latent phase of labor had a successful trial of labor, compared with 61% (.05 less than P less than .10) of patients who had an arrest of dilation in the active phase of labor and 65% (not significant) of those who had an arrest of descent. The only serious complication among study patients was a single instance of uterine scar dehiscence (0.5%). We conclude that approximately two-thirds of patients with a previous cesarean delivery for dystocia will have a successful trial of labor. Of these women, those individuals whose initial operation was performed in the latent phase of labor appear to have the best prognosis for subsequent vaginal delivery.