Gynecomastia is a common clinical problem. The patient’s concerns are: discomfort, aesthetic impact, and suspicion of cancer. The physician’s concern is whether it is the initial manifestation of an insidious tumor or the clinical manifestation of a serious disease and whether it is idiopathic, physiologic or pathologic gynecomastia. It is generally considered abnormal when breast tissue can be palpated during a man’s lifetime, except in three cases (transient mastopexy in newborns, enlargement of the breast during puberty and occasional mastopexy in older men). The growth of the female breast is dependent on the action of estrogen. The administration of estrogen to men also causes breast development and is histologically indistinguishable from other causes of male breast development. Therefore, it can be assumed that all gynecomastia is due to an increase in estrogen production or a decrease in the androgen/estrogen ratio. Excessive estrogen is the main cause of gynecomastia, and the administration of exogenous estrogen preparations to men, such as estrogen therapy in patients with prostate cancer, long-term estrogen use in transsexual men, and excessive estrogen secretion from adrenal or testicular tumors can lead to gynecomastia.