PURPOSE: We studied the controversial relationship of percent free prostate specific antigen (PSA) with organ confined prostate cancer and PSA failure after radical prostatectomy. MATERIALS AND METHODS: We tested the characteristics of the percent free PSA monoclonal Immulite DPC Immunoassay (Diagnostic Products Corp., Los Angeles, California) for predicting organ confinement in 698 consecutive unscreened men treated only with radical prostatectomy between 1995 and 2000. In addition, we assessed the ability of percent free PSA to predict post-radical prostatectomy PSA failure, defined as PSA 0.1 ng./ml. or greater, in a subset of 581 men in whom followup was available. All statistical analyses were repeated for stage T1c cancer with PSA between 2 and 10 ng./ml. RESULTS: On univariate analyses percent free PSA achieved significance for predicting organ confined disease at all clinical stages (p
