Gynecomastia is a common endocrine disorder in which there is a benign enlargement of breast tissue in males. Most adolescent boys, up to 70%, have some breast development during puberty. Newborn and adolescent males frequently experience temporary gynecomastia due to the influence of maternal hormones and hormonal changes during puberty, respectively. The development of gynecomastia is usually associated with benign pubertal changes, but in rare cases may be seen in association with certain disease states. Gynecomastia may be seen in individuals with Klinefelter syndrome or certain cancers, with disorders involving the endocrine system or metabolic dysfunction, with the use of certain medications, or in older males due to a natural decline in testosterone production. In adolescent boys, the condition is often a source of psychological distress; however, 75% of pubertal gynecomastia cases resolve within two years of onset without treatment. Disturbances in the endocrine system that lead to an increase in the ratio of estrogens/androgens are believed to be responsible for gynecomastia development. This may occur even if the levels of estrogens and androgens are both appropriate but the ratio is altered. The disorder is usually diagnosed by a physician after a detailed history and physical examination. Conservative management of gynecomastia is often appropriate as the condition commonly resolves on its own. Medical treatment of gynecomastia that has persisted beyond two years is often ineffective. Medications such as aromatase inhibitors have been found to be effective in some chronic cases, but surgical removal of the excess tissue is usually required.