Four instances (8%) of inflammatory fibroid polyp (IFP) with concomitant adenocarcinoma or adenoma, in the same area, were noted among 50 cases of IFP of the stomach. Adding two cases from other sources, four cases of gastric IFP concomitant with an adenocarcinoma and two of gastric IFP concomitant with an adenoma were studied histopathologically and immunohistochemically. All lesions were located in the gastric antrum and they were restricted to the mucosa in three, and they involved both mucosa and submucosa in the other three. Neither S100 protein nor factor VIII-associated antigen was recognized in the principal component cells, using an immunoperoxidase technique. This finding suggests the conventional view that the proliferating cells were neither neurogenic nor angioblastic, but rather, were fibroblastic in origin. The four concomitant carcinomas were early adenocarcinomas restricted to within the mucosa, and the two concomitant adenomas were tubular adenomas with a moderate epithelial atypia. All these neoplasms were present in or adjacent to the IFP. We emphasize that the IFP, albeit benign, may carry an adenocarcinoma or an adenoma.