The aim of the study was to report the diagnostic performance of total prostate-specific antigen (tPSA) and free prostate-specific antigen ratio (%fPSA). The diagnostic performances of tPSA and %fPSA were evaluated in 364 men by ROC curves, sensitivity, specificity and diagnostic odds ratio calculations. One hundred and sixty-two patients were diagnosed as prostate cancer (PCa) and 202 as normal. The median tPSA levels and %fPSA ratios differed significantly, 11.16 ng/mL and 11 versus 6.51 ng/mL and 20 in PCa and normal groups, respectively. At tPSA levels between 4-10 ng/mL; area under curve (AUC)%fPSA was greater than AUCtPSA. 16 as a cut off value of %fPSA was the optimum choice revealing a sensitivity of 0.703, a specificity of 0.656 and diagnostic odds ratio of 4.254(95% CI 2.157- 8.39 ). %fPSA ratio is an expedient screening marker in PCa. In our laboratory, at tPSA levels between 4- 10 ng/mL, %fPSA ratio of 16 offers a preferable diagnostic performance. [Turk J Cancer 2009;39(1):18-25]