Myeloid sarcoma (MS) is a rare disease that presents as an extramedullary tumor of myeloid cells. Most patients subsequently develop acute myelogenous leukemia (AML), and their prognosis is poor. Here, we report the case of a 28-year-old woman with a primary isolated myeloid sarcoma which originated in the gastrointestinal (GI) tract. Two months after initial presentation, bone marrow tests led to a diagnosis of AML. This case is noteworthy because GI tract infiltration with leukemic cells is very rare, and it is even more rare as an occurrence preceding the development of systemic leukemia.