Over the past years, a growing demand for testosterone replacement therapy in aging men has been noted in the US as well as in Europe. The current evidence for detrimental consequences of low testosterone in old men is largely based on retrospective studies. On the other hand, prospective placebo-controlled randomized trials investigating clinically relevant endpoints are limited. Clinical benefits of testosterone replacement therapy in ageing men include improved sexual function and libido, increase in muscle mass and -function, as well as bone mass accrual. Whether testosterone supplementation in ageing men confers an altered risk for cardiovascular disease and/or prostate cancer remains unclear. Ongoing clinical trials (e. g. TRAVERSE trial, NCT03 518 034) will help to resolve these questions.