Waldenström’s macroglobulinemia is a low-grade lymphoplasmacytic lymphoma characterized by a circulating monoclonal IgM. The clinical manifestations are due to deposition of IgM in liver, spleen, and/or lymph nodes. Related symptoms include anemia and complications of the hyperviscosity syndrome. Renal involvement in classical cases of Waldenström’s macroglobulinemia is rare, and the pathological hallmark finding in the renal biopsy specimen is a thrombotic microangiopathy. We report the case of a 73-year-old female with the diagnosis of pernicious anemia for 2 years before she presented with acute renal failure. A renal biopsy performed suggested the diagnosis of myeloma cast nephropathy. However, bone marrow biopsy specimens and hematological studies did not support this diagnosis. Serum and urinary protein electrophoresis revealed a monoclonal lambda subtype IgM. Ultrasound imaging showed an enlarged spleen. The diagnosis of cast nephropathy in a patient with Waldenström’s macroglobulinemia was made. She underwent treatment with fludarabine and plasmapheresis/hemodyalisis with dramatic improvement of her renal function.