Since its introduction in Sweden in 1994, emergency contraception has become a welcome addition to the campaign against unwanted pregnancy. In addition to an unplanned pregnancy, unprotected sexual intercourse may also involve the risk of contracting sexually transmitted diseases (STD). The aim of this study was to assess the short- and long-term risk of unintended pregnancy and to determine the frequency of chlamydia infections in women receiving emergency contraception. Between September 1998 and February 1999 young women aged 15-25 years had the opportunity to obtain emergency contraception (Yuzpe method) at a youth clinic in the city of Orebro where the opening hours were extended to include Saturdays and Sundays. A follow-up visit 3 weeks after treatment, which included contraceptive counseling, was offered to all participants. At both visits, a pregnancy test and a chlamydia test were performed, and the women completed a questionnaire. After the initial visit, the young women where monitored for new pregnancies during the following 12 months. One pregnancy occurred in the 134 young women who received emergency contraception during the study period. None of the women had a positive chlamydia test. Of those requesting emergency contraception, 54% did so because no contraception was used, 32% because of a ruptured condom, 11% because of missed oral contraceptives (OC), and 5% had mixed reasons. At long-term follow-up 1 year after the initial visit, 10 of the 134 young women had experienced an unplanned pregnancy that terminated in legal abortion in 9 women. All these women had either started and terminated OC or had never commenced the prescribed OC. Young women who request emergency contraception are, despite a planned follow-up with contraceptive counseling, a high risk group for new unintended pregnancies. In Sweden they do not seem to be a high risk group for STD.