Here we describe a case in which a urine-based FGFR3 genetic test, (CertNDxTM Bladder Cancer Assay [Predictive Biosciences, Lexington, MA, USA]) was pivotal in diagnosing an upper urinary tract carcinoma that was difficult to diagnose by cytology or endoscopy. The gene discussed is FGFR3; the disease is urinary bladder carcinoma.