Ewing sarcoma/primitive neuroectodermal tumor is classically a tumor of the soft tissue or bone in children and young adults, but several cases have been described in patients of all ages. Within the last decade, the clinicopathologic spectrum of Ewing sarcoma/primitive neuroectodermal tumor has been markedly expanded by recognition that the tumor may also have a visceral origin. We describe a case of primitive neuroectodermal tumor arising in the stomach of a 66-year-old woman. The neoplasm was excised using a radical surgical procedure. Microscopically, the tumor was made up of solid nests and sheets of round cells. Immunohistochemically, the tumor cells showed immunoreactivity for CD99, S100, neuron-specific enolase, and vimentin. A multiplex real-time polymerase chain reaction assay detected an EWS-ERG fusion. To our knowledge, this is the first description of a primitive neuroectodermal tumor arising in the stomach.