OBJECTIVE To investigate preoperative characteristics that distinguish favourable and unfavourable pathological and clinical outcomes in men with high biopsy Gleason sum (8-10) prostate cancer to better select men who will most benefit from radical prostatectomy (RP). PATIENTS AND METHODS The Institutional Review Board-approved institutional RP database (1982-2010) was analysed for men with high-Gleason prostate cancer on biopsy; 842 men were identified. The 10-year biochemical-free (BFS), metastasis-free (MFS) and prostate cancer-specific survival (CSS) were calculated using the Kaplan-Meier method to verify favourable pathology as men with Gleason <8 at RP or <= pT3a compared with men with unfavourable pathology with Gleason 8-10 and pT3b or N1. Preoperative characteristics were compared using appropriate comparative tests. Logistic regression determined preoperative predictors of unfavourable pathology. RESULTS There was favourable pathology in 656 (77.9%) men. The 10-year BFS, MFS and CSS were 31.0%, 60.9% and 74.8%, respectively. In contrast, men with unfavourable pathological findings had significantly worse 10-year BFS, MFS and CSS, at 4.3%, 29.1% and 52.3%, respectively (all P < 0.001). In multivariable logistic regression, a prostate-specific antigen (PSA) concentration of >10 ng/mL (odds ratio [OR] 2.24, 95% confidence interval [CI] 1.38-3.62, P = 0.001), advanced clinical stage (>= cT2b; OR 2.55, 95% CI 1.55-4.21, P < 0.001), Gleason pattern 9 or 10 at biopsy (OR 2.55, 95% CI 1.59-4.09, P < 0.001), increasing number of cores positive with high-grade cancer (OR 1.16, 95% CI 1.01-1.34, P = 0.04) and >50% positive core involvement (OR 2.25, 95% CI 1.17-4.35, P = 0.015) were predictive of unfavourable pathology. CONCLUSIONS Men with high-Gleason sum at biopsy are at high risk for biochemical recurrence, metastasis and death after RP; men with high Gleason sum and advanced pathological stage (pT3b or N1) have the worst prognosis. Among men with high-Gleason sum at biopsy, a PSA concentration of > 10 ng/mL, clinical stage >= T2b, Gleason pattern 9 or 10, increasing number of cores with high-grade cancer and >50% core involvement are predictive of unfavourable pathology.