BACKGROUND This prospective noncomparative observational study evaluated the clinical aspects of adolescents who received an etonogestrel implant within 6 months of delivery. METHODS The study population comprised 44 adolescents managed at the Family Planning Sector of São Paulo Federal University. The implant was inserted, on average, 102 days after delivery and patients were followed during 1 year. At each monthly visit to the clinic, the participants were weighed, had their blood pressure measured and were asked to report on symptoms experienced during the last 30 days. RESULTS Approximately one-third (38.6%) of the participants reported symptoms, mostly headaches. There were no complaints of dysmenorrhea, breast tenderness or lower leg edema throughout the 12 months of follow-up. Mean body weight dropped 1.2 kg on average, from 56.4 kg at implant insertion to 55.3 kg at the end of the 1-year period. Body mass index also decreased 0.5 kg/m(2) on average, although these changes did not reach statistical significance. Systolic and diastolic blood pressure remained unchanged throughout the study period. There were no pregnancies and none of the participants discontinued the method (528 women-months). CONCLUSIONS These findings suggest that the etonogestrel implant is a safe and effective contraceptive method that is well accepted by adolescents after a pregnancy.