The cases of prostate cancer diagnosed at our hospital after the introduction of transrectal ultrasound-guided prostate biopsy were analyzed to ascertain the cancer detection rate among individuals with a prostate-specific antigen (PSA) below 4.0 ng/ml and to assess the pathological characteristics of the prostatectomy specimens. During the period from January 1997 to December 2003, 1,167 individuals received prostate biopsies at our hospital. Before March 2003, the PSA cut-off level for biopsy was set at 4.0 ng/ml, but a biopsy was sometimes performed if a rectal examination revealed abnormalities or the patient desired a biopsy with a PSA below 4.0 ng/ml. After April 2003, all individuals with a PSA over 3.1 ng/ml were biopsied. The results of the prostate biopsy and the pathology data on radical prostatectomy specimens were compared between individuals with a PSA below 4.0 ng/ml and those with a PSA of 4.1-10 ng/ml. The prostate cancer detection rate among individuals with a PSA between 3.1 and 4.0 ng/ml was 19.4% (12/62) before March 2003 and 15.6% (7/45) after April 2003. The number of cancer-positive core was significantly lower among individuals with a PSA below 4.0 ng/ml. On prostatectomy specimens the percentage of surgical margin positive cases was significantly higher among individuals with a PSA below 4.0ng/ml (17 cases) than those with a PSA of 4.1-10 ng/ml (67 cases), although there was no significant difference between these two groups in terms of the pathological stage and Gleason score. Our results indicate that the prostate cancer detection rate is also high among Japanese men with a PSA below 4.0 ng/ml. The biopsy results and pathological features for prostate cancer with a PSA below 4.0 ng/ml did not differ markedly from prostate cancer with a PSA in the gray zone (4.1-10.0 ng/ml).