Many patients with POEMS syndrome have osteosclerotic plasmacytoma. Radiation therapy is useful for patients who have localized lesions, although chemotherapy is necessary for patients who have widespread lesions. Thus, evaluation of these lesions is important to determine the therapeutic strategy. We evaluated the activities of lesions in two patients with POEMS syndrome by (18)F-FDG positron emission tomography (PET)/computed tomography (CT) scan. In the first patient, PET/CT scan revealed osteosclerotic lesions, which were not detected by Ga-scintigraphy or plain X-ray. It also detected residual disease activity and relapse. In the second patient, lymph node involvement was suggested by (18)F-FDG uptake, and plasmacytoma was confirmed by subsequent biopsy. In the extramedullary lesions of this case, FDG uptake was as marked as in myeloma, whereas bone lesion was only detectable by CT scan. In POEMS syndrome, the PET and CT are complementary, and the combined PET/CT scan is considered to be very useful for evaluation of involved lesions.