Gynecomastia is a common finding in adolescent men. The primary care provider should feel equipped to thoroughly evaluate this condition and to differentiate physiologic from pathologic breast enlargement. The present review focuses on the epidemiology, pathogenesis, evaluation, and treatment of gynecomastia during adolescence.While gynecomastia has long been attributed to an imbalance between estrogen and androgen concentrations, recent literature has begun to illuminate other potential mechanisms for breast development in adolescent men. Increased leptin levels, as well as human chorionic gonadotropin and luteinizing hormone receptors on male breast tissue, may play a role. Newer treatment strategies, such as the antiestrogen raloxifene, have shown promising results; however, further studies are needed to determine long-term efficacy. As a result of the limited pharmaceutical treatment options, many more adolescents are seeking surgical intervention.Gynecomastia is frequently encountered in the primary care setting. During adolescence, male breast enlargement is most often benign and rarely represents a pathologic mechanism. Careful attention should be paid to both the breast and testicular examination. A detailed history should include an inquiry regarding the use of illicit substances, anabolic-androgenic steroids, herbal products, and medications. The impact of gynecomastia on the adolescent's mental health should be assessed. A workup for pathologic causes is rarely required. Reassurance remains the standard of care for physiologic gynecomastia.