We report a case of adenosquamous carcinoma of the stomach. Grossly, the tumor showed "giant gastric folds" involving the fornix and body, and histologically was composed of adenocarcinoma and squamous cell carcinoma components. Both components diffusely proliferated and infiltrated in the gastric wall, mainly in the mucosa and submucosa, where prominent inflammatory changes such as desmoplasia and edema were observed. There were many intermingled foci of both components, and direct transitions between them were frequently observed. Immunohistochemically, adenocarcinoma cells were positive for secretory component and carcinoembryonic antigen and negative for involucrin, while the squamous cell carcinoma component was positive for involucrin and negative for carcinoembryonic antigen. It was suggested in this case that squamous metaplasia might have arisen multifocally in a preexisting adenocarcinoma and that diffuse proliferation and infiltration of carcinoma cells with prominent inflammatory changes in the submucosa might be responsible for the formation of "giant gastric folds".