A case of collision carcinoma (squamous cell carcinoma and Barrett's adenocarcinoma) in the residual cervical esophagus of a 68-year-old woman at 27 years after subtotal esophagectomy for thoracic esophageal carcinoma is reported. The patient initially noticed cervical dysphagia in 2002, but did not seek treatment. In April 2004, the patient was referred to our department by a local physician with the diagnosis of carcinoma of the cervical esophagus. In September 2004, the patient underwent resection of the cervical esophagus and partial resection of the gastric tube combined with cervical lymph node dissection under a diagnosis of double cancer (i.e., metachronous cervical esophageal carcinoma and carcinoma of the gastric tube). Esophagogastric continuity was restored by transplantation of a free jejunal graft with vascular anastomosis. Pathological examination showed squamous cell carcinoma on the esophageal side of the esophagogastric anastomosis and columnar epithelium with a tongue-shaped extension across the anastomotic line that included Barrett's epithelium, as well as adenocarcinoma, on the gastric tube side. The squamous cell carcinoma and adenocarcinoma were contiguous, but there was a distinct border between them and no morphological transition. Immunohistochemical staining showed positivity for p53 in the squamous carcinoma cells, while it was negative in the adenocarcinoma cells. In contrast, HER2 (c-erb-2) was strongly positive in the adenocarcinoma cells, but negative in the squamous carcinoma. Based on these findings, it was concluded that two separate carcinomas had arisen at different sites and grown independently until they collided and merged to form a collision carcinoma.