National University College of Medicine, Seoul, Korea Intravascular large B-cell lymphoma (IVLBCL) is a subtype of diffuse large cell lymphoma, characterized by proliferation of lymphoid cells in the intravascular space of various organs without causing a mass effect. Although 18F-FDG PET is a powerful imaging tool in lymphoma, the usefulness of 18F-FDG PET in the assessment of IVLBCL is still controversial. 99mTc-MIBI, a tumor imaging radiopharmaceutical with a different mechanism from that of 18F-FDG, has been reported to be also effective in lymphoma. However, there is nearly no report on the efficacy of 99mTc-MIBI in the assessment of IVLBCL. We present one case of IVLBCL that showed 99mTc-MIBI accumulation in the involved bone marrow as an incidental finding, which was discrepant from that of 18F-FDG PET. (Nucl Med Mol Imaging 2009;43(4):352-356)