Background: The incidence of small, localised, well-differentiated prostate cancer (PCa) is increasing, mainly as a result of screening. Many of these cancers will not progress, and radical therapy may lead to substantial overtreatment. Active surveillance (AS) has emerged as an alternative. Objective: To retrospectively validate the currently used criteria for eligibility for AS. Design, setting, and participants: For this cohort study, data from 616 men who were diagnosed with PCa between 1994 and 2007 at a mean age of 66.3 yr in four centres of the European Randomized Study of Screening for Prostate Cancer (ERSPC) were combined. All patients fit the criteria for AS (prostate-specific antigen [PSA] <= 10.0 ng/ml, PSA-density <0.2 ng/ml per ml, stage T1C/T2, Gleason score <= 3 + 3 = 6, and <= 2 positive biopsy cores), and initially they were managed expectantly. Median follow-up was 3.91 yr. Measurements: Disease specific-, overall-, and treatment-free survival were studied. Present PSA characteristics were assessed and also compared between men who were switching to deferred active therapy during follow-up and men remaining untreated. Results and limitations: The calculated (Kaplan-Meier) 10-yr PCa-specific survival (21 patients at risk) was 100%, which sharply contrasted with 77% overall survival. Men still alive showed favourable PSA characteristics. Although the calculated 10-yr treatment-free survival was only 43%, objective signs of progression often did not indicate the shift to radical treatment. The cohort consisted of men on AS and those on watchful waiting W; information on comorbidity or psychological distress was not available. Conclusions: AS seems justified in selected men with screen-detected PCa. Prospective protocol-based AS programs are necessary to optimise selection criteria and to find the appropriate trigger points for switching to active therapy. Possible negative psychological reactions with AS against improved quality of life by withholding side-effects from radical treatment should be considered. (C) 2008 European Association of Urology. Published by Elsevier B.V. All rights reserved.