Prostate-specific antigen (PSA) is the most useful tumor marker available today. However, its inability to clearly distinguish between prostate cancer and benign prostatic hyperplasia may result in serial and unnecessary prostate biopsies. Various attempts have been made to improve its specificity. PSA-related parameters including PSA density, PSA density for the transition zone, age- or race-specific PSA reference range, PSA velocity, and percent free PSA are the most promising approaches available at present.