OBJECTIVES: We sought to determine predictors of uterine evacuation for women undergoing medical abortion using mifepristone and vaginal misoprostol through 63 days' gestation. STUDY DESIGN: We pooled data from two prospective multicenter medical abortion trials. In one study, women received mifepristone 200 mg followed either 6-8 or 23-25 h later by misoprostol 800 mcg vaginally. In the second study, women received mifepristone 200 mg followed either <15 min or 23-25 h later by misoprostol 800 mcg vaginally. We examined the absolute risk (AR) of uterine evacuation using Fisher's Exact Tests for categorical variables and Student t test and Wilcoxon rank-sum tests for continuous variables. We used logistic regression to calculate odds ratios (ORs) of uterine evacuation. RESULTS: Uterine evacuation was performed for 75 (3.5%) of 2160 women. In multivariable analysis, 5 or more prior deliveries (AR 11.9%, OR 4.6) and gestational age of 8 weeks or more (AR 4.1%, OR 2.1) were significantly associated with uterine evacuation, while age of 20 years or younger (AR 1.4%, OR 0.4) was significantly and inversely associated with uterine evacuation. Prior cesarean delivery, multiple gestations, smoking, weight, body surface area and body mass index were not predictive of uterine evacuation in univariate or multivariable analysis. CONCLUSION: Uterine evacuation is an uncommon outcome in medical abortion with mifepristone and vaginal misoprostol. Five or more deliveries are the only significant predictor that identifies a group with an AR of uterine evacuation of more than 6%. IMPLICATIONS: Uterine evacuation is uncommon in medical abortion with mifepristone and vaginal misoprostol. Parity of five or more is the only significant predictor of uterine evacuation exceeding 6%. Until additional research is completed, medical abortion should not be withheld from women with five or more deliveries.