Because prostate cancer is diagnosed by blind biopsy, there is underlying uncertainty as to its extent and aggressiveness, evidenced by 40% of cases being upgraded after surgery compared to the diagnostic biopsy. This uncertainty contributes to the overtreatment of low risk localized prostate cancer that fuels the current debate surrounding prostate cancer screening and treatment. This issue presents presents a validated tool that uses clinical variables to predict upgrading of Gleason score 6 prostate cancer. Ideally, this and other tools should increase the acceptance, safety and use of active surveillance in men with localized prostate cancer detected by screening and help to address the problem of overtreatment.