Late-onset hypogonadism (LOH) and testosterone replacement therapy (TRT) are subjects of much recent research. Because aging men are at risk for benign prostatic hyperplasia (BPH) and prostate cancer, elucidating the relationship between testosterone and these diseases is crucial to ensure its safe administration. It is known that testosterone supplementation may worsen active prostate cancer and that its blockade or removal slows the disease’s progression. However, recent studies have attempted to show that, in individuals in whom prostate cancer has been ruled out, TRT may simply restore serum testosterone levels to within normal limits without significant adverse affects on the prostate. Patients undergoing TRT should be monitored carefully for any evidence of prostatic disease.