A 47-year-old man presented with abdominal pain, vomiting, and bone pain. Laboratory findings revealed severe hypercalcemia, anemia, and renal insufficiency with decreased serum parathyroid hormone. FDG PET/CT was performed for characteristics suggestive of multiple myeloma and other occult malignancy. The images revealed widespread osteolytic lesions with only 1 focus of definite abnormal FDG uptake. B-cell acute lymphoblastic leukemia was confirmed by pathological examination following bone marrow biopsy.