T cell factor (TCF)-4 and β-catenin are well recognized as key regulators in many developmental processes. TCF-4 binding with β-catenin can activate the transcriptional activity of downstream target genes (e.g. c-myc and cyclin-D1). Upregulation of TCF/β-catenin activity can promote carcinogenesis in many tissues. However, its precise role in bladder cancer is still unclear. Since typical activating mutations have not been previously reported in the bladder, we examined whether TCF-4 mutations occur in human bladder carcinoma cell lines. In the present study, interestingly, TCF-4 gene mutations were found in human bladder carcinoma cell lines as shown by reverse transcription polymerase chain reaction and a sequencing method. A TCF-4 microsatellite instability (MSI) phenotype was identified to be an (A)8 repeat arising from the deletion of an A in the (A)9 coding repeat. Moreover, immunofluorescence analysis showed that the frameshift mutant of TCF-4 was exclusively localized in the nucleus of bladder cancer cells. Collectively, our data indicate that TCF-4 MSI+ and the expression of spliced forms appear in human bladder cancer cells, and suggest a role of the TCF-4-mediated signal pathway in progression of bladder cancer.