Testosterone is the most potent among the androgens and is found within the body at the highest level. Moreover it is known that this hormone has effects on behaviors and mood. It is thought that testosterone is responsible from regulation of the aggressive behavior and accepted that this function is performed by interaction of serotonin and cortisol. Clinically it is observed that hypogonadal or the testosterone deficiency at elderly men leads to fatigue, decrease of libido, irritability, insomnia, depression and similar neuropsychiatric issues. However such symptoms may be improved by means of Testosterone Replacement Therapy. The relation between depression and testosterone is tried to be explained by means of interaction between the Hypothalamic-Pituitary-Adrenal and the Hypothalamic-Pituitary-Gonadal axes. Early occurrence of the schizophrenia at the men and higher incidences of schizophrenia as well, is the reminder of relation with testosterone. Beside the observation of a negative relation between the severity of negative symptoms and levels of testosterone at male patients with schizophrenia it has not been answered yet whether the low levels of testosterone contribute to the etiology of the disease or hypogonadism is a result of disease process. A negative relation was reported too, between the risk of Alzheimer Disease occurrence and levels of testosterone. All of this data makes think that among the androgens especially the testosterone plays a role in the occurrence of schizophrenia, depression and Alzheimer Disease symptoms as well as regulation of the aggression.