In 156 cases of depressed early gastric cancer in the antrum or corpus, the differences between differentiated and undifferentiated carcinoma were studied by comparing the histological diagnosis of the resected specimens and their endoscopic appearance. We reached the following conclusions: (a) Younger patients more often had undifferentiated carcinoma (mean age: 59.8 years) than differentiated carcinoma (mean age: 77.2 years). (b) One hundred and twenty-five of 156 cases were limited to the mucosa and 29 cases were limited to the submucosa. (c) Undifferentiated gastric cancers more often invaded beyond the mucosa even when the tumor was small than did differentiated tumors. (d) Many differentiated tumors showed a smooth depressed surface, erythema at the edge of the cancer, and tapering of the gastric rugae. (e) In undifferentiated lesions the depressed tumor surface had a varied appearance, with various sized granules and nodules, as well as fading of the mucosal color and fusion of the rugae. It is important at endoscopy to consider not only whether a lesion is benign or a malignant, but also to consider its histological type. In particular, it is vital to detect small, undifferentiated gastric cancers as early as possible.