Superficial spreading type of carcinoma of the esophagus was defined as lesions with intramucosal extension of carcinoma 20 mm or more from the main lesion. Eleven (6.1%) of 179 cases were thus selected for this investigation. These cases were further divided into two groups: Group A, consisting of four cases (2.2%) with the main lesion confined to the submucosa, representing a relatively early stage; and Group B, consisting of seven cases (3.9%) with the main lesion invading the muscular layer or deeper. One of the most characteristic features in the four cases belonging to Group A was an unexpectedly high incidence of lymphatic permeation and lymph node metastases leading to a poor prognosis. Another feature that may be important, particularly for surgeons performing esophagectomy, was the difficulty in deciding the proximal resection line of the esophagus because the boundaries between involved and uninvolved portions were frequently indistinguishable in this particular pathologic entity, not only in Group A but in Group B.