Prostate adenocarcinoma has the highest incidence of any malignancy and is the second leading cause of cancer-related deaths in men in industrialized countries. The development and progression of prostate cancer are dependent on testosterone and dihydrotestosterone; the androgen receptor is the vehicle through which these androgens exert their regulation on prostate cellular proliferation and differentiation. As a result, much effort has been devoted to elucidating the role of the androgen receptor in prostate cancer. The CAG and GGN trinucleotide repeats in exon 1 of the androgen receptor gene have been linked to prostate cancer risk and progression in some studies. Also, androgen receptor gene amplification may be a mechanism of prostate cancer cell adaptation to hormonal therapy. In addition, androgen receptor somatic mutations can result in receptors that have altered binding specificity when compared with wild-type receptors and heightened affinity for hormones other than testosterone and dihydrotestosterone. Gene amplification and somatic mutations, coupled with the fact that various growth factors have been shown to stimulate androgen receptor activity independently of androgens, may enable prostate cancer cells to grow despite testicular-androgen ablation. Unfortunately, current medical therapy for metastatic prostate cancer is deficient, hormone-refractory prostate cancer is a major obstacle in treatment, and, as a result, prostate cancer mortality is still significant. Further study of the function of the androgen receptor will offer a better understanding of prostate cancer pathogenesis and progression, aiding the development of more effective treatments for this disease.