PURPOSE: Percent tumor involvement has been associated with biochemical progression in organ confined disease, although its role in predicting outcome in men with more advanced disease pathology is unclear. We hypothesized percent tumor involvement may be a good correlate of outcome in all stages of prostate cancer. MATERIALS AND METHODS: We examined the association between percent tumor involvement in the radical prostatectomy specimen and the outcome measures of pathological stage and biochemical progression using multivariate logistic regression and Cox proportional hazards analysis, respectively, in 2,220 patients from the Duke Prostate Center radical prostatectomy database. RESULTS: On multivariate analysis, percent tumor involvement significantly predicted the risk of positive margins (p <0.001), extracapsular extension (p <0.001), seminal vesicle invasion (p <0.001) and biochemical progression (HR 1.16, 95% CI 1.01-1.33, p = 0.035). The percent tumor involvement cut points of 5% or less, 6% to 20%, 21% to 50% and greater than 50% significantly separated men in groups with differing biochemical progression risk (p <0.001). In addition, these cut points were further able to stratify men among those with organ confined margin negative disease (p <0.001), either positive margins or extracapsular extension (p <0.001), and those with seminal vesicle invasion (p = 0.02). CONCLUSIONS: Percent tumor involvement was a significant predictor of biochemical progression and was able to further stratify men who were already assigned to narrowly defined pathological groups. If confirmed in other studies, percent tumor involvement may enable the clinician to identify the high risk patient who stands to benefit the most from adjuvant therapy.