Prostate specific antigen(PSA) is a serine protease produced by both benign and malignant prostatic epithelium that can be measured in serum samples by immuoassay. Although recent studies suggest that serum PSA may be useful in the early detection of prostate cancer, it is known that PSA elevations occur in men with benign prostatic hyperplasia and that men with prostate cancer can have normal PSA leveL We evaluated serum prostate specific antigen and pathologic findings on patient with benign prostatic hyperplasia. The most significant factor affecting high serum PSA levels in patient with B.P.H. was P.I.N. Identification of PIN will be helpful to detect early prostatic cancer because PIN is consid- ered a precursor of prostatic cancer.