Prostate cancer accounts for about 25% of all the newly diagnosed cancers in American men and was projected to cause >28 000 deaths in 2008. Black men are disproportionately affected; their incidence rate is about 1.6 times greater than the rate for white men. As the population ages, the number of new cases per year is expected to increase by >60% and reach 300 000 by 2015. This high incidence, coupled with the protracted onset of the disease, makes PCa a particularly appropriate candidate for prevention and early intervention strategies. Potential disease precursors, particularly high-grade prostatic intraepithelial neoplasia, might help identify men at high risk of developing PCa. Dihydrotestosterone, a product converted from testosterone by 5 alpha-reductases, plays an important role in normal prostate growth and in the development of PCa. The 5 alpha-reductase levels, particularly type 1, appear to increase during the disease course of prostatic intraepithelial neoplasia and PCa, with greater expression occurring as the disease progresses. Therefore, the inhibition of 5 alpha-reductase could potentially reduce the risk of PCa development, slow or prevent disease progression, and/or treat existing disease. A substantial research effort has recently focused on understanding the pathways involved in the disease's emergence and progression, particularly the 5a-reductase pathway. UROLOGY 73 (Suppl 5A): 4-10, 2009. (C) 2009 Published by Elsevier Inc.