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Activating somatic point mutations in exons 7, 10, and 15 of the FGFR3 gene are frequently observed in urothelial cell carcinoma (UCC) (1)(2). These mutations have been found primarily in superficial papillary pTa tumors and were absent in carcinoma in situ (3). Given the high frequency of FGFR3 mutations and the possible implication of this receptor in the development of UCC, it was important to develop a simple, fast, and reliable method to identify these mutations in greater detail as a potential tool for the diagnosis and follow-up of UCC patients. Ten different FGFR3 mutations have been described in UCC, but 4 of them (R248C, S249C, G372C, and Y375C) account for >95% of cases (2). These mutations therefore represent an excellent target for assays, such as allele-specific PCR (AS-PCR), that depend on the specific detection of point mutations. The general principle underlying the AS-PCR technique is to design a mutation-specific primer that produces the preferential amplification of a specific mutant allele (4). We compared the results obtained with this assay with those obtained by direct sequencing in a series of 95 DNA samples extracted from UCC tumors. We also analyzed matching tumors and voided urine from 20 patients. Our results demonstrate the sensitivity, specificity, and reliability of this technique for detecting FGFR3 mutations in both tumors and urine from patients with UCC. Ninety-five primary tumor samples were collected from patients admitted to the Department of Urology of Hospitals Henri Mondor (Creteil) and CHRU (Besancon) and who had received no previous treatment. Patients gave written informed consent, and we collected matched tumors and blood samples. Tumors from each patient were snap-frozen and stored at −80 °C. DNA from tumor samples was extracted as described previously (5). DNA was extracted from the blood with use of the QIAamp system …