Some patients with splenic angiosarcoma initially manifest thrombocytopenia owing to hypersplenism or tumor-related bone marrow fibrosis. The diagnosis of bone marrow metastasis in patients with splenic angiosarcoma is challenging, as the presentation mimics idiopathic thrombocytopenic purpura or primary myelofibrosis. Our case showed diffuse FDG uptake in the vertebral bodies, sacroiliac bone, humerus, femur, and clavicles. It was pathologically diagnosed as bone marrow metastasis of splenic angiosarcoma. We believe that the heterogeneous FDG accumulation in the bone marrow, although nonspecific, can be useful for the diagnosis of the bone marrow metastasis in patients with splenic angiosarcoma.