Androgens are reported to be actively produced in situ in human prostate cancer. These locally produced androgens are also demonstrated to play important role in the pathogenesis and development of human prostate cancer. The status of locally produced androgen inactivation and metabolism, however, remains unclear. Therefore, it is important to examine the status of this in situ androgen metabolism and inactivation in order to improve clinical response to endocrine therapy in the patients diagnosed with prostate cancer. 17beta-hydroxysteroid dehydrogenase type 11 (Pan1b) was demonstrated to display greatest activity with 5alpha-androstan-3alpha, 17beta-diol (3alpha-diol) as substrate in several human androgen metabolizing tissues, suggesting that this enzyme may play important role in androgen metabolism. However, its details including the expression level of Pan1b have not been studied in human prostate cancer. In this study, we evaluated immunolocalization of Pan1b in human prostate cancer specimens obtained from surgery (n=40), and correlated the findings with clinicopathological features of the patients in order to study its clinical significance. Pan1b immunoreactivity was detected in 19 cases (48%) and was significantly associated with cancer of seminal vesicle invasion (P<0.05). Theses data suggest that Pan1b expression could be connected with advanced prostate cancer.