BACKGROUND: Previous emergency contraception studies have excluded women who report>1 episode of unprotected or underprotected intercourse. Thus, clinical recommendations are based on exposure to a single episode of underprotected intercourse. OBJECTIVE: We sought to assess the prevalence and timing of underprotected intercourse episodes among women requesting emergency contraception and to examine the probability of pregnancy following an emergency contraception regimen including placement of either a copper intrauterine device or a levonorgestrel intrauterine device with simultaneous administration of an oral levonorgestrel pill in women reporting multiple underprotected intercourse episodes, including episodes beyond the Food and Drug Administration-approved emergency contraception time frame (6-14 days). STUDY DESIGN: Women seeking emergency contraception who had a negative pregnancy test and desired either a copper intrauterine device or levonorgestrel emergency contraception regimen enrolled in this prospective observational study. At enrollment, participants reported the number and timing of underprotected intercourse episodes in the previous 14 days. Two weeks later, participants reported the results of a self-administered home pregnancy test. RESULTS: Of the 176 women who presented for emergency contraception and received a same-day intrauterine device, 43%(n = 76) reported multiple underprotected intercourse episodes in the 14 days prior to presenting for emergency contraception. Women with multiple underprotected intercourse episodes reported a median of 3 events (range 2-20). Two-week pregnancy data were available for 172 (98%) participants. Only 1 participant had a positive pregnancy test. Pregnancy occurred in 0 of 97 (0%; 95% confidence interval, 0-3.7%) women with a single underprotected intercourse episode and 1 of 75 (1.3%; 95% confidence interval, 0-7.2%) women reporting multiple underprotected intercourse episodes; this includes 1 of 40 (2.5%; 95% confidence interval, 0-13.2%) women reporting underprotected intercourse 6-14 days prior to intrauterine device insertion. CONCLUSION: Women seeking emergency contraception from clinics commonly reported multiple recent underprotected intercourse episodes, including episodes occurring beyond the Food and Drug Administration-approved emergency contraception time frame. However, the probability of pregnancy was low following same-day intrauterine device placement.