Hypogonadism is highly prevalent in the elderly and in men with prostate cancer. Symptoms of hypogonadism, such as depression, lack of libido, and decreased bone mineral density, can significantly impair quality of life. In addition, testosterone plays an important role in erectile preservation and in growth and function of the cavernosal and penile nerves. There are compelling data showing that testosterone replacement therapy (TRT) does not increase the risk of prostate cancer. The literature (four published studies) concerning men treated with TRT after definitive therapy for prostate cancer reports only one biochemical recurrence. Based on these data, physicians cannot really justify withholding TRT from symptomatic patients after they have been successful treated for prostate cancer. This review gives the practising urologist an overview of the latest literature and useful advice on this controversial topic.