Prostate cancer is the most common urological malignancy in Taiwan. The formation of prostate cancer has been reported to be associated with androgen. Two key steps in the sex steroid synthesis are mediated by the enzyme cytochrome p450c17alpha which is encoded in the CYP17 gene. Our aim was to investigate whether a polymorphism of CYP17 gene could be used as a genetic marker for associating prostate cancer. In this study, we compared the frequency of the C/T polymorphism of CYP17 gene 5'-UTR promoter region between 93 patients with prostate cancer and 121 healthy male volunteers (age, >60 years). The result revealed no significant association between the CYP17 genotype and prostate cancer (P =.781). Therefore, CYP17 C/T polymorphism is not a valid genetic marker for prostate cancer. Although a possible interaction between CYP17 gene C/T polymorphism and SP-1 transcription factor has been reported in the literature, we did not find any evidence for this the difference among clinical staging, pathological grading, or responsiveness to hormonal therapy in prostate cancer.