Testosterone regulates male sexual development and body composition. In adult men, testosterone levels exhibit a gradual decline with increasing age. Whether it is age per se or health and behaviour related factors that are responsible for this decline, and the implications thereof for subsequent health remain controversial. Observational studies report associations of lower testosterone levels with poorer health outcomes in ageing men, including frailty, reduced sexual activity, insulin resistance and cardiovascular events and mortality. However, outcome data from randomised clinical trials of testosterone are limited, and are lacking for major endpoints such as cardiovascular events. The risks and benefits of testosterone intervention in older men require further clarification. This article will review the role of testosterone in men, discuss epidemiological and interventional data illuminating its potential role to preserve health during male ageing, consider the limitations of the evidence base and implications for clinical practice, and explore future directions for research in this topical area.