We identified predictors for bone-marrow [18F]FDG uptake and MR signals among complete blood count, C-reactive protein (CRP), and anthropometric factors, and demonstrated the bone-marrow physiology using integrated [18F]FDG-PET/MRI. 174 oncology patients without bone-marrow lesions underwent whole-body [18F]FDG-PET/MRI. The standardized uptake value (SUV), apparent diffusion coefficient (ADC), proton density fat-fraction (PDFF), and a reciprocal of T2* relaxation time (R2*) were measured in lumbar vertebrae (L3-5) and bilateral ilia. Vertebrae, pelvis, and ribs were evaluated by 3-point visual scoring on DWI. The association of the PET/MR features with the predictors was examined. Multi-regression analyses identified CRP as the strongest predictor for lumbar and iliac SUVs (standardized coefficient: β = 0.31 and β = 0.38, respectively), and for lumbar and iliac R2* (β = 0.31 and β = 0.46, respectively). In contrast, age was the strongest factor influencing lumbar and iliac ADCs (β = 0.23 and β = 0.21, respectively), and lumbar and iliac PDFFs (β = 0.53 and β = 0.54, respectively). Regarding DWI-visual scores, age was the strongest predictor for vertebrae (β = - 0.47), and the red cell distribution width (RDW) was the strongest predictor for pelvis and ribs (β = 0.33 and β = 0.47, respectively). The bone-marrow [18F]FDG uptake and R2* reflect anemia of inflammation (increased granulopoiesis and reduced iron metabolism), whereas bone-marrow DWI and PDFF reflect age and anemia-responsive erythropoiesis.