BACKGROUND Concern about the risk of upper genital tract infection (pelvic inflammatory disease) often limits use of the IUD, a highly effective contraceptive. Prophylactic antibiotic administration around the time of induced abortion significantly reduces the risk of postoperative endometritis.(Sawaya, 1996) Since the risk of IUD-related infection is limited to the first few weeks to months after insertion,(Lee, 1983; Farley, 1992) contamination of the endometrial cavity at the time of insertion(Mishell, 1966) appears to be the mechanism, rather than the IUD or string itself. Thus, antibiotic administration before IUD insertion might reduce the risk of upper genital tract infection from passive introduction of bacteria at insertion. OBJECTIVE To assess the effectiveness of prophylactic antibiotic administration before IUD insertion in reducing IUD-related complications and discontinuations within three months of insertion. The primary outcome was pelvic inflammatory disease (four reports) or early removals of the device (two reports). METHODS We searched both MEDLINE and EMBASE, handsearches of journals through CENTRAL, and lists of references. We also wrote to international experts in the field to identify unpublished studies. METHODS We included randomized controlled trials using any antibiotic compared with a placebo. We found four such trials; two had pilot study data available. METHODS METHODS We used searches of MEDLINE, EMBASE, and handsearches of journals available through CENTRAL. We also reviewed lists of references in original research and in review articles. We wrote to experts to identify unpublished trials and made telephone calls to authors to supply missing information. Two independent reviewers abstracted data. We assessed the validity of each study using methods suggested in the Cochrane Handbook. RESULTS We generated 2x2 tables for the principal outcome measures. We used the Peto modified Mantel-Haenszel technique to calculate odds ratios and assessed statistical heterogeneity between studies. RESULTS The odds ratios for pelvic inflammatory disease associated with use of prophylactic doxycycline or azithromycin compared with placebo or no treatment was 0.89 (95%CI 0.53-1.51). Use of prophylaxis was associated with a small reduction in unscheduled vists to the provider (OR 0.82; 95% CI 0.70-0.98). Use of doxycycline or azithromycin had little effect on the likelihood of removal of the IUD within 90 days of insertion (OR 1.05; 95% CI 0.68-1.63). Significant heterogeneity did not exist between studies. CONCLUSIONS Use of either doxycycline 200 mg or azithromycin 500 mg by mouth before IUD insertion confers little benefit. While the reduction in unscheduled visits to the provider was marginally significant, the cost-effectiveness of routine prophylaxis remains questionable. A uniform finding in these trials was the low risk of IUD-associated infection, with or without use of antibiotic prophylaxis.