A case of carcinosarcoma arising from the intraepithelial spreading area of esophageal squamous cell carcinoma (SCC) is reported herein. A 64-year-old man was referred to our hospital for investigation of a sore throat and dysphagia. An endoscopic examination revealed a 2. 5-cm polypoid mass in the mid-esophagus. Esophagograms taken 1 month prior to consultation by our hospital and just before surgery revealed marked change within a period of less than 2 months from a 2-cm sessile elevated mass to a 4-cm polypoid mass with a lobular appearance. The resected specimen contained two lesions in the esophagus. The larger one measured 4.0 x 2.0 x 2.0 cm and had a pedunculated polypoid shape, while the smaller one, measuring 1 cm in diameter, was a plateau-type elevated lesion located 3 cm distal from the larger mass. Histologically, the distal smaller lesion was diagnosed as primary SCC associated with a high frequency of intraepithelial spread, while the larger polypoid mass was composed of spindle-shaped sarcomatous cells, arising from the intraepithelial spread of SCC. To our knowledge, this is the only reported case of esophageal carcinosarcoma arising from an area of intraepithelial spread of SCC that showed such surprisingly rapid growth.