To examine the histogenesis and progression of esophageal squamous cell carcinoma, 76 cases of a primary squamous cell carcinoma were reviewed retrospectively, and 16 lesions of squamous cell carcinoma of the esophagus less than 1.0 cm in diameter were studied histopathologically. None of the patients had received radiation therapy preoperatively. Among 16 foci, 13 were intraepithelial carcinomas, and three were restricted to within the mucosa. In two patients with a solitary, minute cancer, there were no associated areas of dysplasia. In 11 patients with multiple primary minute foci, seven contained 14 areas of dysplasia in the esophagus. There was no continuity between the minute foci of carcinoma and areas of dysplasia. These findings are interpreted to mean that dysplasia is a "subcancerous" lesion rather than a "precancerous" one and that various degrees of lesions such as dysplasia and carcinoma occur multicentrically in the same esophagus. The sequence of dysplasia to carcinoma must be examined using the techniques of molecular biology.