Abstract Purpose: To improve the specificity in prostate cancer diagnosis and to prevent unnecessary prostate biopsies, especially in the serum prostate-specific antigen (PSA) “gray zone” between 3 and 15 ng/mL, the implementation of prostate cancer–specific markers is urgently needed. The recently discovered prostate cancer antigen 3 (PCA3) is such a promising prostate cancer marker. In a previous single institution study, the PCA3 urine test clearly proved to be of diagnostic value. Therefore, the diagnostic performance of the PCA3 urine test was validated in a multicenter study. Experimental Design: The first voided urine after digital rectal examination was collected from a total of 583 men with serum PSA levels between 3 and 15 ng/mL who were to undergo prostate biopsies. We determined the PCA3 score in these samples and correlated the results with the results of the prostate biopsies. Results: A total of 534 men (92%) had an informative sample. The area under the receiver-operating characteristic curve, a measure of the diagnostic accuracy of a test, was 0.66 for the PCA3 urine test and 0.57 for serum PSA. The sensitivity for the PCA3 urine test was 65%, the specificity was 66% (versus 47% for serum PSA), and the negative predictive value was 80%. Conclusions: In this multicenter study, we validated the diagnostic performance of the PCA3 urine test in the largest group studied thus far using a PCA3 gene-based test. This study shows that the PCA3 urine test, when used as a reflex test, can improve the specificity in prostate cancer diagnosis and could prevent many unnecessary prostate biopsies.