Accurate assessment of the lesion after treatment of patients with bone lymphoma is difficult. In this patient who demonstrated complete remission after chemotherapy, the regions of fluorine-18 fluorodeoxyglucose (18FFDG)PET uptake diminished more rapidly following therapy, indicating a complete response at much earlier stage than did Magnetic Resonance Imaging (MRI) or CT based findings. With the conventional methods, such as MRI and CT, it was difficult to assess whether the residual tumor tissue was viable or not. Decision to complete response is very important in patients with lymphoma to plan the further treatment. We experienced a patient with primary lymphoma of bone who revealed complete response to chemotherapy on 18FFDGPET while CT showed persistent destructive bone lesion. Thus, 18FFDGPET study after therapy may be superior to CT in the evaluation of response to treatment in primary lymphoma of bone.