The esophagus was totally examined in 264 autopsied cases and 61 operated cases, for a total of 325 cases, to clarify the histogenesis of squamous cell carcinoma of the esophagus. Epithelial dysplasia of the mucosa was present in 27% and subclinical carcinoma was found in 2.4%. Hyperplasia of the duct of the esophageal gland proper was present in 34% and cysplasia of the ductal epithelium in 3%. Reserve cell hyperplasia-like change of the islet of the ectopic gastric mucosa was found in 4% and reserve cell hyperplasia-like change of the esophagogastric junction zone in 13%. Of the seven cases of microcarcinoma, two showed dysplasia and gradual transition and one presented dysplasia and abrupt transition. Another two were considered to have originated in the ductal epithelium. These findings suggested that they could all be the sites of origin of cancer development.