Although the routine use of serum PSA testing has undoubtedly increased prostate cancer detection, one of its main drawbacks has been its lack of specificity, which results in a high negative biopsy rate. Consequently, a large population of men with chronically elevated serum PSA and one or more negative biopsies has emerged. More accurate tests are needed that can help identify which patients are at high risk of developing prostate cancer, and for whom repeat prostate biopsies are mandatory. To improve the specificity of prostate cancer diagnosis, prostate-cancer-specific markers, such as prostate cancer gene 3 (PCA3), are needed. The strong association between PCA3 mRNA overexpression and malignant transformation of prostate epithelium indicates its potential as a diagnostic biomarker. Quantification of PCA3 mRNA levels in urine was found to help predict the outcome of prostate biopsies. The intensive and time-consuming reverse-transcriptase polymerase chain reaction PCA3 urine test has been translated successfully into the fast and easy transcription-mediated amplification (TMA)-based PCA3 test. This test is the first RNA-based molecular diagnostic assay in body fluids for prostate cancer that is available to urologists. This Review describes the translation of the molecular marker PCA3 from the research laboratory to clinical practice.