Gynecomastia is common problem in teenager and adults, generally due to imbalance in hormonal physiology like increase the action of estrogen than androgenic action at the site of breast glandular tissue. Most of the patients may suffer pubertal gynecomastia or breast glandular enlargement, caused by medication, decreased production of testicular hormone or may be idiopathic causes. Gynecomastia must be differentiated from pseudogynecomastia as well as breast cancer, the causes of gynecomastia can be found out through patient history, Physical examination and blood test. This article mainly focused on the etiology, pathophysiology, epidemiology, histology and diagnosis of gynecomastia