Objective: To estimate the effect of increased body weight and body mass index (BMI) on pregnancy rates with levonorgestrel (LNG) 1.5 mg used as emergency contraception (EC). Methods: The study reviewed data from 6873 women in four WHO-HRP randomized trials on EC conducted between 1993 and 2010. Participants took either 1.5 mg of LNG as a single dose or in two doses 12 h apart, up to 120 h of unprotected intercourse. Contraceptive efficacy (pregnancy rates) at different weight and BMI categories was evaluated. Results: Overall pregnancy rate was low at 1.2%. Pregnancy rates were also low in women weighing over 80 kg (0.7%) and who were obese (BMI over 30 kg/m(2)) (2.0%). The pooled analyses for pregnancy demonstrated that BMI over 30 kg/m2 decreased efficacy significantly (odds ratio 8.27, 95% confidence interval = 2.70-25.37) when compared to women in lower BMI categories, mainly influenced by pregnancies in obese women from one study site. Sensitivity analyses excluding that site showed that obesity was no longer a risk factor; however, the other studies included too few obese women in the sample to exclude a substantial decrease in efficacy. Conclusions: Pregnancy rates with use of LNG 1.5 mg for EC were low at less than 3% across different weight and BMI categories. Pooled analyses showed an increase in pregnancy rates among obese women (BMI more than 30 kg/m(2)) compared to women with normal BMI levels, influenced by pregnancies all coming from one study site. (C) 2016 Published by Elsevier Inc.