We reviewed 10 patients with esophageal mucosal carcinoma in order to improve the early diagnosis of the disease. Histologically seven of the 14 lesions were carcinomas in situ (epithelial cancer), and the other seven lesions were carcinomas confined to the mucosa other than epithelial cancer (muscularis mucosae cancer), all 14 lesions were squamous cell carcinomas (SCC). One of these seven mucosal SCC, which demonstrated an extensive spreading-type SCC in which the size of the SCC was 7 cm long while extending entirely around the esophageal lumen in circumferential spread, is described in detail, and multiple epithelial cancers existed separately in one case. Eleven lesions diagnosed before operation showed abnormal findings on conventional endoscopy regardless of the size and depth of transmural invasion. An additional lesion was visible with dye endoscopy as an unstained area, but it was not visible with radiography or conventional endoscopy. Dye endoscopy using Lugol solution is very important because it allows detection and evaluation of the extent of esophageal mucosal cancer.