Specific treatments targeted toward oncogenes expressed in cancer cells are currently under development. Patients with urothelial carcinomas showing HER-2/ neu (human epidermal growth factor receptor 2) overexpression are candidates for such a specific treatment (trastuzumab). However, to be effective, this therapeutic approach requires an extremely reliable evaluation of HER-2/ neu status in tumors. In order to assess the status of expression of this gene and to optimize its assessment, we analyzed a series of 64 primary urothelial carcinomas using immunohistochemistry (IHC) with the CB11 monoclonal antibody coupled with fluorescent in situ hybridization (FISH) in 21 cases. Strong HER-2/ neu overexpression was detected using IHC in 15 of the 64 (23%) cases analyzed, and this rate rose to 33% for patients with metastases. HER-2/ neu overexpression, as revealed using IHC, is strongly associated (95%) with gene amplification assessed using FISH. Patients with urothelial carcinomas overexpressing HER-2/ neu using IHC are potential candidates for targeted chemotherapy.