Testosterone is a natural hormone which is an essential factor to maintain the physical and emotional well-being in men, regardless of age. Male hypogonadism is an endocrinal condition of testosterone deficiency with the potential to cause multiple physical complaints and psychosocial problems. The condition can be of primary (due to testicular injury), secondary (due to diseases of the hypothalamus or pituitary gland) or functional nature (due to comorbidities, such as inflammatory diseases, obesity, type 2 diabetes mellitus). Testosterone deficiency causes problems of a sexual nature, promotes metabolic disequilibrium and can impair physical abilities (reduction in muscle mass, increase in fat mass). In addition, in the condition of hypogonadism depression, osteoporosis and/or anemia often develop. A testosterone replacement therapy should not be initiated in cases of a desire to have children, unclear processes of the prostate glands or mammary glands or an elevated hematocrit value. The diagnosis as well as treatment and monitoring of the treatment should follow the international guidelines and then a clear improvement in the abovenamed complaints can be expected. Particularly functional hypogonadism, which is mostly but not exclusively diagnosed in older men, always requires treatment of the underlying comorbidity prior to starting testosterone administration.