The progressive aging of the population and the wish to keep a good quality of life in advanced ages makes testosterone deficit syndrome associated with aging a health issue of increasing relevance. It is a proved fact there is a decrease of androgen levels associated with aging. Nevertheless, there are some difficulties to establish what is the actual prevalence, since there are some ambiguities about which clinical and biochemical parameters allow us to state a correct clinical diagnosis. The figures on prevalence are variable, specially taking into consideration the different age ranges found in the studies, but we could say there would be a global prevalence of around 6% to 12% of symptomatic hypogonadism in the age range between 30/40 and 70 years, with a progressive increase with age There is a series of factors that may favor androgen deficit increasing the prevalence in different population groups. The main factors are those entities related with metabolic syndrome (obesity, hyperglycemia (insulin resistance,high blood pressure and dyslipemia) in addition to chronic diseases such us AIDS, cancer, and certain pharmacological treatments.