Objective: To compare the efficacy of misoprostol 50 mu g vaginally and 50 mu g sublingually for labor induction at term. Materials and Methods: One hundred and sixty women were randomized to receive misoprostol 50 mu g vaginally ( n = 80) or 50 mu g sublingually misoprostol ( n = 80). The doses were given every 4 h ( maximum 6 doses). Primary outcome measure was number of cesarean deliveries. Induction to delivery time, delivery within 24 h, the number of misoprostol doses given; the need for oxytocin augmentation, tachysystole and uterine hyperstimulation rates and neonatal outcomes were secondary outcome measures. Results: The mean induction to delivery time was 748 +/- 379 min in the vaginal group and 711 +/- 425 in the sublingual group ( p = 0.56). The number of women delivering within 24 h was 73 (91.3%) in the vaginal group and 74 ( 92.5%) in the sublingual group ( p = 0.78). The mean number of misoprostol doses required was significantly higher in the sublingual group (1.9 +/- 1.2) compared with the vaginal group (1.1 +/- 0.4; p < 0.001). More women in the sublingual group experienced tachysystole ( n = 14, 17.5%) compared with the vaginal group ( n = 3, 3.8%; p = 0.005). Seven cases (8.8%) in the vaginal group and 12 cases in the sublingual group (15%) required emergent cesarean delivery for fetal heart rate abnormalities ( p = 0.22). Other neonatal outcomes including umbilical artery pH, Apgar scores and intensive care unit admission were similar in the two groups. Conclusion: Sublingual misoprostol is as efficacious as vaginal misoprostol for induction of labor. More frequent tachysystole is observed with misoprostol 50 mu g sublingually, but neonatal outcomes are similar. Copyright (C) 2005 S. Karger AG, Basel.