A total of 114 cases, consisting of 20 non-cancerous esophagi, 48 non-irradiated cancerous esophagi, and 46 irradiated cancerous esophagi, were investigated with semiserial sections to evaluate the role of epithelial dysplasia as a precursor of esophageal cancer. The incidence of dysplasia was higher in cancerous esophagi than in non-cancerous esophagi and in non-irradiated cancerous esophagi than in irradiated cancerous esophagi. The difference in distribution pattern of dysplasia made it possible to classify the esophagi into three types: extensive, multifocal, and scanty. In the extensive type the main tumor tended to have an ill-defined margin and large diameter. In the multifocal type it tended to be superficial and small, and in the scanty type it usually had a well-defined margin. A possible relationship of epithelial dysplasia to the origin of esophageal cancer and its growth was shown by at least two thirds of the esophageal cancers.