As men grow older, testosterone levels fall, with a steeper decline in unbound or free testosterone compared with total testosterone concentrations. Lower testosterone levels have been associated with poorer cognitive function, and with impaired general and sexual health in aging men. Recently, lower testosterone levels have been linked with metabolic syndrome and type II diabetes, both conditions associated with cardiovascular disease, and shown to predict higher overall and cardiovascular-related mortality in middle-aged and older men. However, reverse causation has to be considered, as systemic illness may result in reduced testosterone levels. Thus, the strength of these associations and the likely direction of causation need to be carefully considered. Furthermore, these conditions may overlap, for example aging, lower testosterone levels, erectile dysfunction and cardiovascular disease are interrelated. Cross-sectional and longitudinal observational studies may be informative. However, ultimately randomized controlled trials of testosterone therapy are needed to clarify its role in the maintenance of general and sexual health in aging men. Testosterone therapy should be considered in hypogonadal men who meet rigorous criteria for the diagnosis of androgen deficiency. Additional consideration should be given to designing and testing interventions that may prevent or ameliorate the age-related decline in testosterone levels in men.