ABSTRACT Introduction: Prostate - specific antigen (PSA) is a useful biomarker for detection of prostate cancer (PCa) and for risk classification in addition to TNM classification and Gleason score (GS). We reported the role of PSA in patients with low (< 20 ng / mL) and extremely high (≥ 100 ng / mL) PSA levels. However, it is unclear whether a correlation exists between middle range PSA levels (20 – 100 ng / mL) at diagnosis and prognosis. Materials and Methods: Between January 2000 and December 2014, 1873 patients underwent prostate biopsy at Kanazawa University Hospital. Of 802 patients who were diagnosed with PCa, 148 patients with middle range PSA levels (20 – 100 ng / mL) were retrospectively analyzed. Results: The percentage of patients with T3 – 4 consistently increased as PSA levels increased from 20 to 100 ng / mL. Although the percentage of patients with GS ≥ 8 or metastases increased as PSA levels increased up to approximately 70 ng / mL, there was no significant increase between 70 and 100 ng / mL. PCa - specific and castration - resistant PCa - free survivals were adversely associated with PSA levels up to 70 ng / mL, but not between 70 and 100 ng / mL. Conclusion: PSA is a useful biomarker for predicting prognosis at levels between 20 and 70 ng / mL. However, PSA cannot be used as a prognostic factor in patients with PCa and PSA levels ≥ 70 ng / mL. When the PSA level reaches approximately 70 ng / mL, prognosis might bottom and reach a plateau.