An unusual case of synchronous gastric carcinomas occurred in a 28-year-old man with a family history of gastric disease. Two tumor foci were identified: a well-differentiated advanced carcinoma with the phenotypic properties of complete intestinal metaplasia and an early intestinal-type carcinoma. Histochemical and immunohistochemical stains to demonstrate complete intestinal metaplasia, ie, Alcian blue pH 2.5/periodic acid-Schiff, high iron diamine/Alcian blue pH 2.5, CD10, and MUC2, were all positive in the advanced adenocarcinoma. Of all markers used, only high iron diamine/Alcian blue pH 2.5 and Alcian blue pH 0.5 were positive in the early carcinoma. In these cases, mistakes frequently are made during examination of endoscopic biopsies. Fortunately, the advanced adenocarcinoma was low grade (the patient has shown no signs of disease at 6 years postsurgery). Histopathologic, histochemical, and immunohistochemical findings suggest that an extensive substrate of complete intestinal metaplasia (corpus) and of complete and incomplete intestinal metaplasia (antrum) can be associated with two independent tumors with different phenotypes.