The fall in testosterone levels with age appears to be a real phenomenon. Declining testicular function and hypothalamic dysregulation appear to be the mechanisms explaining the fall in testosterone levels with age. The increased prevalence of obesity and chronic illness in ageing men both cause a large drop in testosterone levels independent of ageing. Age-related hypogonadism appears to be different to other 'classical' causes of hypogonadism. Testosterone levels are not unequivocally low and associated symptoms are non-specific. In frail older men with low testosterone levels, testosterone therapy appears to improve QOL and physical function. In less frail men, however, effects of testosterone therapy in the ageing male are small and/or inconsistent. There remains an urgent need for randomised clinical trials with sufficient size, duration and power to determine specific benefits and risks of testosterone therapy in older men.