Background: The aim of this study was to compare 11 active surveillance (AS) protocols in contemporary European men treated with radical prostatectomy (RP) at the Martini-Clinic Prostate Cancer Center. Patients and Methods: Analyzed were 3498 RP patients, from 2005 to 2016, who underwent ≥ 10 core biopsies and fulfilled at least 1 of 11 examined AS entry definitions. We tested proportions of AS eligibility, ineligibility, presence of primary Gleason 4/5, upstage, and c ombinations thereof at RP, as well as 5-year biochemical recurrence-free survival (BFS). Results: The most and least stringent criteria were very low risk National Comprehensive Cancer Network and Royal Marsden with 18.8% and 96.1% of AS-eligible patients, respectively. Rates of primary Gleason 4/5 at RP, upstaging, or both features, respectively, ranged from 2.3% to 6.7%, 6.1% to 18.2%, and 7.1% to 21.0% for those 2 AS entry definitions. The range of individuals deemed AS-ineligible between the same 2 AS entry definitions, despite not harboring unfavorable pathology (primary Gleason pattern 4/5, upstage, or both), was 80.3% to 3.7%, 78.3% to 3.4%, and 77.8% to 3.4%, respectively. BFS rates showed narrow variability, with a range of 85.9% to 91.8%. Conclusion: Use of stringent AS entry definitions reduces the number of AS-eligible patients, which is related to a select range in individual entry parameters. Moreover, rates of unfavorable pathology at RP as much as tripled between most and least stringent AS entry definitions. However, less stringent AS entry definitions result in the lowest AS-ineligibility rates, in men without unfavorable pathology. BFS rates were virtually invariably high. Clinicians should know differences in key parameters underlying each AS entry definition, associated effect on rates of eligibility, and potential misclassification of individuals. © 2017 Elsevier Inc.