Purpose To evaluate the outcomes of active surveillance (AS) on patients with low-risk prostate cancer (PCa) and to identify predictors of disease reclassification. Methods In 2005, we defined an institutional AS protocol (Sorveglianza Attiva Istituto Nazionale Tumori [SAINT]), and we joined the Prostate Cancer Research International: Active Surveillance (PRIAS) study in 2007. Eligibility criteria included clinical stage ≤T2a, initial prostate-specific antigen (PSA) <10 ng/mL, and Gleason Pattern Score (GPS) ≤3 + 3 (both protocols); ≤25% positive cores with a maximum core length containing cancer ≤50% (SAINT); and ≤2 positive cores and PSA density <0.2 ng/mL/cm³ (PRIAS). Switching to active treatment was advised for a worsening of GPS, increased positive cores, or PSA doubling time <3 years. Active treatment-free survival (ATFS) was assessed using the ­Kaplan-Meier method. Factors associated with ATFS were evaluated with a multivariate Cox proportional hazards model. Results A total of 818 patients were included: 200 in SAINT, 530 in PRIAS, and 88 in personalized AS monitoring. Active treatment-free survival was 50% after a median follow-up of 60 months. A total of 404/818 patients (49.4%) discontinued AS: 274 for biopsy-related reclassification, 121/404 (30%) for off-protocol reasons, 9/404 (2.2%) because of anxiety. Biopsy reclassification was associated with PSA density (hazard ratio [HR] 1.8), maximum percentage of core involvement (HR 1.5), positive cores at diagnostic biopsy (HR 1.6), older age (HR 1.5), and prostate volume (HR 0.6) (all p<0.01). Patients from SAINT were significantly more likely to discontinue AS than were the patients from PRIAS (HR 1.65, p<0.0001). Conclusions Five years after diagnosis, 50% of patients with early PCa were spared from active treatment. Wide inclusion criteria are associated with lower ATFS. However, at preliminary analysis, this does not seem to affect the probability of unfavorable pathology.