Micro-ribonucleic acids (miRNAs) are small noncoding RNAs that posttranscriptionally regulate gene expression. The ability of miRNAs to inhibit translation of oncogenes and tumor suppressors implies that they may be involved in carcinogenesis. Our review focuses on the potential of urinary miRNAs to serve as biomarkers of urologic cancers. We discuss in detail the recent knowledge about the origin of urinary miRNAs, their stability, quality control, and their utility as a potential new class of biomarkers in urologic cancer. Finally, we summarize the studies focusing on detection and characterization of urinary miRNAs as potential biomarkers in bladder, prostate, and kidney cancers.