38 Background: Due to the inability to predict progression and need for treatment, patients with low-risk prostate cancer (LRPC) managed by active surveillance (AS) are subjected to repeated biopsies and their possible complications. We developed a nomogram predicting the risk of progression in patients on AS for LRPC. Methods: A retrospective review of all patients enrolled in an AS program at Memorial Sloan-Kettering Cancer Center (MSKCC) between 1993 and 2012 was conducted. Demographic, clinical, and pathologic data for patients who met the inclusion criteria for AS (cT1 or cT2a, prostate-specific antigen [PSA] less than 10, Gleason 6 or less, no more than three positive biopsy cores and no greater than 50% involvement of any single core) on the diagnostic and the confirmatory biopsies were collected and used to develop a nomogram for predicting progression-free probability. Multivariable logistic regression analysis was used to model the association between each risk variable (age, PSA levels, clinical stage, biopsy features) and disease progression. Progression was defined as failure to meet the inclusion criteria during follow up. Results: A total of 1,095 patients were enrolled in an AS program at MSKCC during the study period, of which 680 met the inclusion criteria for AS on both the diagnostic and the confirmatory biopsies and had available follow-up. At a median follow-up of 3 years 101 patients progressed. A nomogram predicting the progression-free probability was designed based on characteristics at diagnosis, result of a confirmatory biopsy and the number of negative and positive surveillance biopsies to date. A concordance index of 0.596 was calculated. Conclusions: Conditioned upon external validation, this nomogram can be used to counsel patients on their risk of progression and their surveillance protocol can be adjusted appropriately, possibly avoiding unnecessary biopsies and preventing biopsy-related complications.