The process of aging in man involves a lot of functional and structural changes in the body organs and systems. In this review we shall characterize the physiological and clinical manifestations of andropause. We'll review the physiological basis of the ageing process, the age-related changes in the testosterone secretion regulation, and the dynamics of androgen action and active testosterone metabolism. We also investigate the multifactorial etiology of age-related physiological changes--the body undergoes changes in its structure, there is a loss of muscle strength and decline in physical functions. Sexual dysfunction, hypogonadism and psychological changes are also commonly observed symptoms in this condition. Changes of similar kind can also be seen in young males with androgen deficiency. The age-related changes in physiological functions can potentially lead to some important consequences such as reduced physical activity, higher risk of developing specific diseases (ischemic heart disease, diabetes, osteoporosis), diminished capacity to recover after acute diseases, but most often it leads to increased fracture predisposition. All these may eventually affect negatively the self-care capacity of patients making them require a long-term professional care, and lead to severe psychological and social isolation and increased mortality and change in quality of life. To limit the age-related physiological decline in serum testosterone levels, we should be able to tackle the still unresolved important clinical issue--can hormone replacement therapy administered to elderly men improve their functional status, prevent diseases from developing, improve quality of life and reduce fracture risk. The data included in the present review will contribute to determining the potential benefits and risks of testosterone replacement therapy.