Objective: To identify predictors of adverse outcome in pregnant women at term receiving 50 mug of intravaginal misoprostol for labor induction. Study design: A prospective observational study was conducted of 720 pregnant women at term with an unfavorable cervix and a medical or obstetric indication for labor induction. All patients received 50 mug of intravaginal misoprostol every 4 h up to three doses. The primary outcome measure was "adverse outcome" defined as: neonatal death, fetal acidemia and emergent cesarean delivery performed for non-reassuring fetal heart rate tracings. A stepwise logistic regression analysis was used to identify predictors of adverse outcome. Results: Tachysystole (frequent uterine contractions) (odds ratio (OR), 3.7; 95% confidence interval (CI), 1.2-10.8) and fetal tachycardia (OR, 4.8; 95% CI, 1.4-16.2) were determined as significant predictors of adverse outcome. The specificity of the model was 94.2%, whereas the sensitivity was 20.4%. Conclusion: In the absence of tachysystole and fetal tachycardia, an uneventful delivery might be expected for women receiving 50 mug of intravaginal misoprostol. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.