Testosterone is a natural hormone which is essential to maintain physical and emotional well-being in men. Male hypogonadism is an endocrine condition of testosterone deficiency with the potential to cause multiple morbidities and psychosocial complaints. The condition can be of primary, secondary or so-called functional origin. Testosterone deficiency can cause symptoms of a sexual nature, augment metabolic dysfunctions and impair physical abilities. A supplementation of testosterone should not be initiated in cases of desired paternity. In this case other treatment modalities must apply. Diagnosis and treatment as well as surveillance of the treatment of hypogonadism are clearly regulated by international guidelines and replacement therapy has been proven to be effective.