Objective. To estimate the incidence of dystocia among nulliparous women without apparent co-morbidity and to examine maternal and fetal short-term outcomes after dystocia. Design. A multi-center cohort study with prospectively collected data. Setting. Nine obstetric departments with annual birth rates between 850 and 5,400. Population. Low-risk nulliparous women in term spontaneous labor with a singleton fetus in cephalic presentation. Methods. Follow-up of 2,810 nulliparas using self-administered questionnaires supplemented with clinical records. Criteria for dystocia. Cervical dilatation ≤2 cm over four hours during the first stage of labor or no descent during two hours (three hours with epidural analgesia) in the descending phase of second stage or no progress for one hour during the expulsive phase of the second stage. Inclusion took place between May 2004 and July 2005. Main outcome measures. Incidences of dystocia, maternal, and fetal outcomes. Results. The cumulative incidence of dystocia was 37% and of the diagnoses 61% were given in the second stage of labor. Women with dystocia treated by augmentation had more cesarean and ventouse deliveries, more often non-clear amniotic fluid, more post-partum hemorrhage and their children were more often given low one-minute neonatal Apgar scores as compared to women delivered without a diagnosis of dystocia. Conclusions. A dystocia incidence of 37% was found in healthy term nulliparas with no indication for induction or elective cesarean delivery. The adverse maternal and neonatal birth outcomes may be related to the cause of dystocia or to augmentation of labor and this question calls for further studies.