Normal testosterone level is influencing all the steps of the male psychosexual development: intrauterine neonatal and final psychosexual development.. At pubertal stage, the quality of testosterone secretion is conditioning the development of the mature male phenotype. In adult life, eugonadism sustains desire, arousal, determines spontaneous erections, facilitates stimulated erection, influencing the response rate to medication. Moreover, eugonadism sustain daydreaming and phantasies, both needed for a normal sexual life. The pathogenic mechanism of all these actions is presented. Talking about hypogonadism means not only the classical types of hypogonadism: due to classical testicular disease of central, hypothalamic and hypophysis disease, but also the partial testosterone deficiency induces by aging (late onset hypogonadism), weight increase (up to 30% of males with metabolic syndrome and 50% of males with diabetes) or secondary hypogonadism described in chronic use of steroids or after long exposure to stress, especially in young males. All these types of hypogonadism, that affect young, middle aged or old males will be presented separately. A therapeutic approach that is individualized for each type of hypogonadism, should consider positive and possible negative effects and all alternatives will be presented: life style changes, sustained weight loss, increase exercise, supplemental therapy, pro fertility treatment.