It is believed that much of the small increased risk for developing pelvic inflammatory disease (PID) associated with the use of an intrauterine device (IUD) appears to be caused by bacterial contamination of the endometrial cavity at the time of insertion. Previous research suggests that use of prophylactic antibiotics immediately prior to IUD insertion may reduce the risk of developing PID. This paper presents results from a randomized clinical trial of 1485 women in Ibadan, Nigeria evaluating the effectiveness of 200 mg of doxycycline (versus placebo) given orally at the time of IUD insertion in reducing the incidence of PID during the first three months of IUD use. Rate of PID infection in the doxycycline-treated group was not significantly lower than that in the placebo-treated group. The rate of unscheduled IUD-related visits to the clinic also was not significantly lower among the doxycycline-treated group. However, the incidence of PID was low (21 cases) for both study groups. Aseptic conditions during IUD insertion, follow-up visits with short intervals to monitor health, and treatment of opportunistic infections may have reduced the potential of PID within this population.