Background: The goal of this study was to investigate ERBB2 (HER2) gene amplification and protein expression in bladder urothelial carcinoma. The HER2 status of 40 patients with transurethral resection or cystectomy was investigated. All cases were analyzed for both HER2 overexpression using immunohistochemistry and HER2 gene amplification using fluorescence in situ hybridization. Eighteen cases had a HER2 score-0 or score-1 (45%), 10 cases had a score-2 (25 %), and 12 cases had a score-3 (30%) with immunohistochemistry. HER2 gene amplification was observed in 16 out of 40 cases (40%). HER2 overexpression and gene amplification were correlated to a high histological grade (P< 0.0001), stage (P