Objective To evaluate the effectiveness of an educational intervention in adolescent health designed for general practitioners, in accordance with evidence-based practice in continuing medical education. Design Randomized, controlled trial with baseline testing and 7- and 13-month follow-ups. Setting The intervention was delivered in local community settings to general practitioners in metropolitan Melbourne, Australia. Participants A total of 108 self-selected general practitioners. Intervention A multifaceted educational program (2.5 hours per week for 6 weeks) in the principles of adolescent health care, followed 6 weeks later by a 2-hour session of case discussion and debriefing. Outcome measures Objective ratings of videotaped consultations with standardized adolescent patients and self-completion questionnaires were used to measure general practitioners' knowledge, skill, and self-perceived competency; satisfaction with the program; and self-reported change in practice. Results 103 of 108 physicians (95%) completed all phases of the intervention and evaluation protocol. The intervention group showed significantly greater improvements than the control group in all outcomes at the 7-month follow-up (all subjects P<0.03), except for the standardized patients' rating of rapport and satisfaction (P=0.12). 104 participants (96%) found the program appropriate and relevant. At the 13-month follow-up, most improvements were sustained, the standardized patients' rating of confidentiality fell slightly, and the objective assessment of competence further improved. 106 physicians (98%) reported a change in practice attributable to the intervention. Conclusions General practitioners were willing to complete continuing medical education in adolescent health and its evaluation. The design of the intervention, using evidence-based educational strategies, proved effective and expeditious in achieving sustainable and large improvements in knowledge, skill, and self-perceived competency.