Background: To inform decisions about active surveillance, we determined the incidence of upgrading and upstaging for a contemporary cohort of low-risk prostate cancer patients who received radical prostatectomy and identified clinical predictors of advanced disease. Methods: We studied 10,273 patients in the Surveillance, Epidemiology, and End Result (SEER) database diagnosed with low-risk prostate cancer (cT1c-T2a, PSA<10 ng/mL and Gleason 3+3=6) in 2010-2011. Upgrading was defined as pathologic Gleason score 7-10 and upstaging as pathologic T3-T4/N1 disease. Regression coefficients were used to evaluate the predictive value of clinical factors for upgrading or upstaging. Significant factors were used to develop a risk stratification table to evaluate individual patients. Results: At prostatectomy, 44% of patients were upgraded and 9.7% were upstaged. Multivariable analysis showed age, PSA, and percent total cores positive were associated with advanced disease (all p<0.001). When these variables were dichotomized by the median, age >60 (Adjusted Odds Ratio [AOR] 1.39), PSA>5.0 (AOR 1.28), and >25% total cores positive (AOR 1.76) were significantly associated with upgrading (all p<0.001). Similarly, age>60 (AOR 1.42), PSA>5.0 (AOR 1.44), and >25% total cores positive (AOR 2.26) were associated with upstaging (all p<0.001). Sixty percent of low-risk patients with PSA 7.5-9.9 and >25% total cores positive were upgraded. Conclusions: A significant proportion of low-risk patients eligible for active surveillance were harboring more aggressive or locally-advanced prostate cancer. Age, PSA and percent total cores positive should be used to assess risk of upgrading or upstaging and can guide decisions to pursue further evaluation or treatment.