Background: This study was performed to reconsider the efficacy of transrectal ultrasonography (TRUS) in diagnosing prostate cancer by analyzing the results of a digital rectal examination (DRE), serum prostate-specific antigen (PSA) and a transrectal ultrasonography in patients with prostate specific antigen levels of 10 ng/ml or less. Materials and Methods: One-hundred and eighty one men with PSA levels of 10 ng/ml or less, who had a TRUS-guided tissue biopsy performed, were included in this study. The detection rate of prostate cancer was compared according to the TRUS result and the presence or absence of nodularity and the consistency of the prostate on DRE. Results: In a total 181 patients, there were 73 patients with PSA levels of 4 ng/ml or less and 4 of them had prostate cancer. Thre were 108 patients with PSA levels of 4-10 ng/ml and 18 of them were prostate cancer. TRUS was performed in 152 patients and 16 out of 58 patients diagnosed with prostate cancer, 3 out of 39 diagnosed with suspicious prostate cancer, and 2 out of 55 patients diagnosed as having no prostate cancer were found to have prostate cancer. In 40 patients, a nodule was palpated on DRE and 8 of them were found to have prostate cancer. Five out of 19 patients with a stony hard consistency, 3 of 12 with a firm to hard consisency, 12 of 129 with a firm consistency, 0 of 13 with a soft to firm consistency, and 2 of 8 with a soft consistency were prostate cancer. In the prostate cancer patients, there were 4 patients with PSA levels of 4 ng/ml or less and all these patients were diagnosed with prostate cancer or suspicious prostate cancer on TRUS but the nodule was not palpated in all patients. Two were soft and 2 were firm consistency on DRE. Conclusion: In patients with serum PSA levels of 10 ng/ml or less, TRUS is a more useful supporting method than DRE and a more active application of TRUS may lead to an early diagnosis and pertinent treatment of prostate cancer.