Urinary 8-hydroxydeoxyguanosine (8-OHdG) level is an oxidative stress marker in patients with cancer; however, little is currently known about the clinical relevance of urinary 8-OHdG levels in patients with prostate cancer at diagnosis. Voided urine samples were collected from patients at the time of prostate biopsy and stored at -80˚C after centrifugation. All of the patients were classified according to histology of the biopsy. Once the patients were diagnosed with prostate cancer, the standard of care and treatments were administered according to the standard guidelines. The association between clinicopathological parameters and urinary 8-OHdG and N-terminal telopeptide (NTx) levels were explored. A total of 409 patients received prostate biopsy, of which 190 were benign, 41 were diagnosed with prostatitis and 178 were diagnosed with prostate cancer. The urinary 8-OHdG/creatinine ratio was marginally associated with prostate size (P=0.052) but not with serum prostate-specific antigen levels (P=0.707). With correction for prostate size, the ratio of urinary 8-OHdG/creatinine was significantly higher in patients with prostate cancer than those without malignancy (P=0.004). Moreover, urinary 8-OHdG levels were weakly associated with urinary NTx levels (r2=0.04, P=0.009). In conclusion, urinary 8-OHdG levels normalized for prostate volume may reflect prostate cancer risk and could be used to predict prostate cancer aggressiveness.