Endoscopic ultrasonographic (EUS) images of 174 cases of gastric cancer were examined to assess the depth of tumor invasion. Comparison was made between the depth of the changes shown in the multi-layered image produced by ultrasonography and the actual depth of invasion. Cases showing ultrasonographic changes extending deeper than the actual tumor were found to have fibrosis associated with peptic ulceration within the tumor focus. In such cases the echo images chiefly depicted the form and nature of the fibrosis, and the images were so characteristic that they could be classified into patterns. In the other cases the depth of tumor invasion could be almost precisely determined by detecting to which layer the changes shown by EUS extended.