The monograph is devoted to the male reproductive system. The diseases are presented in detail and sequentially according to the new classification proposed in recent years. For the first time in Bulgaria, the harmful effects of the environment on the male reproductive system, in particular oxidative stress, are examined in detail, as well as the problem of effective control of the use of doping hormone preparations. Special attention is paid to puberty and the so-called male menopause. The monograph is intended for endocrinologists, internists, urologists, pediatricians, and general practitioners. It is also of interest to specialists in sports medicine and doping control.