Androgens are essential for prostatic growth and development, but also play a significant role in the pathogenesis of prostate disease. The traditional view that higher testosterone levels represent a risk factor for prostate cancer (PCa) appears to have little evidentiary support. Some studies have described a relationship between lower testosterone levels and more advanced disease. Serum androgen levels, within a broad range, are thus suggested to show no association with PCa risk, whereas low rather than high serum testosterone levels have been found to be associated with advanced or high-grade disease at the time of PCa diagnosis. Dihydrotestosterone, the principal prostatic androgen, is transformed from testosterone by type 1 and type 2 5alpha-reductase, and therapeutic benefits may thus be potentially achieved through the inhibition of 5alpha-reductase.