BACKGROUND Most patients undergoing Roux-en-Y gastric bypass (RYGB) are women in reproductive age. It is not known if bariatric surgery affects the pharmacokinetics of oral contraceptives. OBJECTIVE The primary objective was to evaluate ethinylestradiol (EE) and levonorgestrel (LNG) absorption in women undergoing RYGB, compared with nonoperated controls matched by age and body mass index (BMI). A secondary objective was to assess whether the time since surgery and BMI in the postoperative period influenced the absorption parameters. METHODS University hospital, Brazil. METHODS This study was designed to compare the maximum plasma concentration (Cmax), the time to the peak plasma level (Tmax), the area under the curve (AUC0-8 and AUC0-∞) after a single dose of a combined oral contraceptive with 0.03 mg EE and 0.15 mg LNG among 20 women after RYGB and 20 controls. Blood samples were obtained for 8 hours. RESULTS The mean LNG AUC0-8 and LNG AUC0-∞ were higher in RYGB group (P = .048 and P = .004, respectively). We found a positive correlation for LNG AUC0-8 (P = .045) and AUC0-∞ (P = .004) and the time since surgery, and we found a negative correlation for LNG Cmax (P = .018), AUC0-8 (P = .003), and AUC0-∞ (P = .001) and BMI. CONCLUSIONS No significant differences were found in oral EE pharmacokinetics. The operated group showed higher mean LNG AUC0-8 and AUC0-∞ but it was not considered clinically significant. The present study suggests that RYGB may not affect EE and LNG absorption.