Gynecomastia is a common and sometimes distressing condition that may occur in males of all ages. Although most cases have benign causes and many are self-limited, male breast enlargement may also be a sign of underlying systemic disease or drug toxicity. Although rare, male breast cancer must also be considered in the differential diagnosis. A careful diagnostic evaluation should be pursued, tailored to the individual patient's circumstances. Treatment may include reassurance, medication, or surgery.