Purpose: Increased FDG uptake in the bone marrow has been reported in patients taking erythropoietin or granulocyte-colony stimulating factor (G-CSF). The aim of this study is to investigate the correlation between F-18 FDG uptake in the bone marrow and bone marrow finding, hematological parameters. Materials and Methods: Twenty patients who had diffuse FDG uptake at the bone marrow and received hematological examinations, bone marrow biopsy within 10 days before or after PET/CT were enrolled in this study. Among them, 11 patients were excluded; 4 patients received G-CSF or erythropoietin before PET/CT. Seven patients showed definite pathology in a bone marrow biopsy. The parameters included the measurement of WBC, hemoglobin, platelet and cellularity of the bone marrow. Results: Bone marrow FDG uptake was correlated with a low hemoglobin but not WBC, platelet. Histopathologic findings in marrow biopsies were various: normal finding (n=3), hyperplasia of granulocytic cells (n=2), eosinophilic hyperplasia (n=1), reactive lymphoid nodules (n=1), hypercelluar marrow (n=1), hypocelluar marrow (n=1). All patients except two, showed normal marrow celluarity. Conclusion: FDG uptake by bone marrow correlated with anemia but not WBC, platelet, bone marrow cellularity. (Nucl Med Mol Imaging 2009;43(1):35-39)