Obesity is not a simple condition which only concerns weight gain, rather it is one of the major disease entities. Treating obesity will be the most effective way of reducing many types of chronic diseases including hypertension, diabetes, atherosclerosis, cardiovascular and cerebrovascular diseases, and peripheral artery diseases. The major cause of obesity is attributed to westernized high calorie diet and exercise deficit, however the aging process and its related hormonal deficiency seems to be the more important factors among the elderly population. Growth hormone deficiency along with sex hormone deficiency, which each progresses with aging process, will either directly or indirectly influence weight gain. In this review, articles on studies of whether sex hormone deficiency can affect weight gain will be reviewed and also whether its replacement through treatment can help reduce weight.