Acute renal failure (ARF) due to bilateral parenchymal infiltration of a high grade malignant non-Hodgkin B-cell lymphoma is exceptional. Early identification of this pathology causing ARF is critical as early induction therapy with cyclophosphamide and prednisone often leads to a substantial recovery of kidney function. This striking case illustrates the usefulness of noninvasive fluoro-deoxy-glucose positron emission tomography/computed tomography as a functional imaging modality demonstrating not only the cause of unexplained ARF but also its convenience for the restaging management of non-Hodgkin lymphomas during complete remission.