Acute myelogenous leukemia (AML) is a hematological disorder that is characterized by an abnormal proliferation of immature myeloid cells. Dedifferentiated and well-differentiated liposarcomas are the two pathological subtypes of liposarcoma, based on the WHO classification. Transition from well-differentiated to dedifferentiated liposarcoma is a well-recognized phenomenon. Well-differentiated tumors are known to have low malignancy grade. However, when dedifferentiation occurs, the tumor acquires the aggressive features of a fully malignant lesion. This process largely is believed to progress in a time-dependant manner; however, time is not the only factor of importance. The potential roles of other factors in this transition are still unclear. To date, the coexistence of AML and liposarcoma has not been reported in the literature. In this paper, we report on a case of coexistence of AML and liposarcoma, and on the unusual behavior of a well-differentiated tumor after dedifferentiation occurs.