BACKGROUND: The optimal selection of prostate cancer (PCa) patients for active surveillance (AS) is currently being debated. OBJECTIVE: To assess the impact of urinary prostate cancer antigen 3 (PCA3) score as an AS criterion instead of and in addition to the current criteria. DESIGN, SETTING, AND PARTICIPANTS: We prospectively studied 106 consecutive low-risk PCa patients (prostate-specific antigen [PSA] ≤10ng/ml, clinical stage T1c-T2a, and biopsy Gleason score 6) who underwent a PCA3 urine test before radical prostatectomy (RP). MEASUREMENTS: Performance of AS criteria (biopsy criteria, PCA3 score, PSA density, and magnetic resonance imaging [MRI]findings) was tested in predicting four prognostic pathologic findings in RP specimens: (1) pT3-4 disease; (2) overall unfavourable disease (OUD) defined by pT3-4 disease and/or pathologic primary Gleason pattern 4; (3) tumour volume<0.5cm(3); and (4) insignificant PCa. RESULTS AND LIMITATIONS: The PCA3 score was strongly correlated with the tumour volume in a linear regression analysis (p<0.001, r=0.409). The risk of having a cancer ≥0.5cm(3) and a significant PCa was increased three-fold in men with a PCA3 score of ≥25 compared with men with a PCA3 score of<25 with most AS biopsy criteria used. There was a trend towards higher PCA3 scores in patients with unfavourable and non-organ-confined disease and Gleason>6 cancers. In a multivariate analysis taking into account each AS criterion, a high PCA3 score (≥25) was an important predictive factor for tumour volume ≥0.5cm(3) (odds ratio [OR]: 5.4; p=0.010) and significant PCa (OR: 12.7; p=0.003). Biopsy criteria and MRI findings were significantly associated with OUD (OR: 3.9 and 5.0, respectively; p=0.030 and p=0.025, respectively). CONCLUSIONS: PCA3 score may be a useful marker to improve the selection for AS in addition to the current AS criteria. With a predictive cut-off of 25, PCA3 score is strongly indicative for tumour volume and insignificant PCa.