Objective: To determine adverse events and discontinuation of Implanon in healthy Thai women between 16 and 45 years of age. Design: Prospective descriptive study. Setting: Family Planning Unit, Department of Obstetrics and Gynecology, Faculty of Medicine, Chiang Mai University. Subjects: Ninety-two female volunteers with eligible criteria, no contraindication for hormonal contraceptive and wished to have long term contraception were recruited. Main outcome measures: Determination of adverse events was done three months after Implanon insertion. Discontinuation of Implanon use was reviewed during the study period of one year. Results: Amenorrhea (40.2%) and infrequent bleeding (39.1%) were the most menstrual adverse events. While most non-menstrual adverse events were headache/dizziness (27.2%) and lower abdominal pain (23.9%). Severe non-menstrual side effect was rare (1-2%). Seven subjects (7.6%) discontinued using Implanon during the one year period of study. Conclusion: Implanon demonstrated a high continue rate at the first year of insertion. It produced similar adverse events like other progestin-only contraceptives. Counseling before insertion is important for increased client satisfaction and a higher continuation rate.