Carcinosarcoma of the tongue is a rare malignancy and its molecular aspect is unclear. A case of carcinosarcoma of the tongue in a 51-year-old man is presented. A polypoid tumor of the tongue, measuring 12 x 12 x 6 mm, was resected. Histologically, the tumor was composed of a squamous cell carcinoma and a spindle cell sarcomatous component. We previously showed that one cell-cycle regulator, the cyclin D1 gene, was frequently amplified in esophageal carcinosarcoma, which shows the same morphologic features as carcinosarcoma of the tongue. In this case, we examined whether the cyclin D1 gene is amplified in carcinosarcoma of the tongue as well. Fluorescence in situ hybridization analysis revealed that the cyclin D1 gene was amplified in both components of carcinosarcoma of the tongue. The cyclin D1 protein was also detected by immunostaining in both components. Our results suggest that the amplification of cyclin D1 gene plays a role in the molecular pathogenesis of carcinosarcoma of the tongue, at least in some cases.