Granulocyte colony-stimulating factor (G-CSF)-producing tumors are malignant tumors associated with a poor prognosis, and G-CSFproducing liposarcoma is particularly rare. We report a case of G-CSF-producing dedifferentiated liposarcoma. 18 F-FDG PET/CT showed abnormal 18 F-FDG uptake throughout the bone marrow and in the primary site. When a diffuse bone marrow 18 F-FDG uptake was observed on 18 F-FDG PET/CT, G-CSFproducing dedifferentiated liposarcoma should be included in the differential diagnosis.