Objective: To evaluate safety and efficacy of levonorgestrel-releasing contraceptive implants (Norplant; Leiras Oy, Turku, Finland) in developing countries. Methods: We used controlled cohort methodology. Women attending family planning clinics in eight developing countries selecting Norplant were enrolled, together with women of similar age choosing intrauterine devices (IUDs) or surgical sterilization. Participants were interviewed and examined at semi-annual visits and followed-up for 5 years regardless of change of contraceptive methods. Incidence rate ratios of health events were estimated for initial and current method use. Results: Altogether, 7977 women initiated Norplant, 6625 IUD, and 1419 sterilization. The overall follow-up rate was 94.6% and 78,323 woman-years of observation were accumulated. Pregnancy rates for Norplant, copper IUDs, and sterilization each averaged less than 1 per 100 woman-years. With two exceptions, no significant excess risk of serious morbidity was detected for Norplant users compared with controls. The incidence of gallbladder disease was higher in women who initiated Norplant use than in controls (rate ratio 1.52, 95% confidence interval [CI] 1.02, 2.27), as was the incidence of hypertension and borderline hypertension in current implant users (rate ratio 1.81; CI 1.12, 2.92). Other new findings were increased risks of respiratory diseases and decreased risks of inflammatory disease of the genital tract in Norplant users compared with IUD users and sterilized women. Conclusion: The study confirms the safety with respect to serious disease and the high contraceptive efficacy of Norplant, copper IUDs, and sterilization.