We evaluated the role of free prostate specific antigen (f-PSA) serum level and its related parameters in detecting prostate cancer. This retrospective study was conducted between January 2006 and March 2008. Transrectal ultrasound guided prostate biopsy was performed for 107 patients who had total PSA (t-PSA) level of either >4 ng/mL with or without palpable nodule or ≤4 ng/mL with palpable nodule on digital rectal examination. The performance measurements for f-PSA, percent free PSA (%f-PSA) and free PSA density (f-PSAD) were determined and compared with those for t-PSA and total PSA density (t-PSAD). Descriptive statistics for all variables of interest were calculated, and receiver operating characteristic curves were generated. Nine patients (8.4%) had normal histology, 69 patients (64.4%) had benign disease and 29 patients (27.1%) had prostate cancer. The performance of f-PSA in PCa detection was better than other evaluated parameters. The largest area under the curve for patients in the gray area (t-PSA range 4.1-10 ng/mL) was for f-PSA, with a value of 0.64 and a sensitivity and specificity of 44% and 87%, respectively. For %f-PSA, these values were 0.59, 63% and 62%, respectively. For patients with a t-PSA level of 10.1-20 ng/mL, they were 0.68, 67%, and 81%, respectively, for f-PSA, and 0.64, 67%, and 76%, respectively, for %f-PSA. In conclusion, f-PSA serum levels performed better than free to total PSA ratio and t-PSA for prostate cancer screening. It is of clinical value which could affect the biopsy decision avoiding unnecessary interventions.