This 3-year study investigating the contraceptive efficacy and tolerability of Implanon in 635 volunteers demonstrates that it was well tolerated and had excellent, reversible, contraceptive efficacy. No pregnancies (Pearl index, 0; 95% CI 0.0-0.2) occurred during 1,200 woman-years of exposure. Irregular bleeding, mainly frequent and prolonged, was the primary reason for discontinuation (19.0%). Infrequent bleeding (29-51%) was the most common bleeding disturbance. Adverse events, other than bleeding irregularities, were generally mild to moderate in intensity and resulted in 9.3% of discontinuations. Over 85% of women with dysmenorrhea at baseline noted an improvement at the end of treatment, while 4% reported new or worsened symptoms. The most commonly reported non-bleeding adverse events were breast pain (16%), acne (12.6%), vaginitis (12%) and pharyngitis (10.5%). However, acne present at enrolment improved or disappeared during treatment in 59% of women. Less than 5% of women experienced implant site symptoms after insertion or removal, mainly mild pain of short duration. Average insertion and removal times were 2.2 and 5.4 min, respectively. In most women, menses returned to normal within 3 months of implant removal. Of those using no contraceptive method, 13.8% became pregnant within 90 days. Implanon represents a highly effective contraceptive option for women.