Gynecomastia (GM) is a polyetiological syndrome characterized by hyperplastic  breast glands in men. Basing on current literature data, the review provides facts on the causes of GM development including physiological and pathological ones. The features of pathology development in various clinical situations including hormone testing, instrumental examinations and karyotyping are considered in detail. An important place is given to the algorithm of GM different forms consistent diagnosis. The problem of the GM medications is discussed separately. The GM various forms differentiation allows determine those patients differentiated management tactics.