Myeloid sarcoma is an extramedullary solid neoplasm composed of myeloid precursor cells. This tumor usually occurs simultaneously with or following the onset of acute leukemia. Rarely, it can be the first manifestation of acute myeloid leukemia. The tumor can occur anywhere in the body. However, primary involvement of the stomach without evidence of leukemia is exceedingly rare, and to the best of our knowledge, imaging features of isolated myeloid sarcoma of the stomach have not been reported in children. This case illustrates the imaging appearances of isolated myeloid sarcoma that initially manifested as gastric submucosal wall thickening and discusses the differential diagnosis, in a 15-year-old girl without evidence of hematologic malignancy.