We experienced a case of relapsed malignant lymphoma with multiple bone marrow or bone lesions. The case was diagnosed as follicular lymphoma by cytological biopsy of the right iliac bone, with (67)Ga scintigraphy showing abnormal, intense uptake in multiple bones. After about 10 months of systemic chemotherapy, a relapse was suspected because of pain in the bilateral legs and a high level of lactate dehydrogenase. Assessment of the lesions in the patient was difficult by computed tomography because the affected sites were localized mainly in the bone marrow. (18)F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) was useful for detecting accurately the relapse sites in the bone marrow and enabled us to determine the field for radiotherapy. There are only a few reports of FDG-PET findings for such bone marrow malignant lymphomas. Therefore, we report the findings of FDG-PET for this case and review some of the literature about bone marrow lymphomas.