Waldenström's macroglobulinemia (WM) is a rare lymphoid neoplasia, accounting for 2% of all hematological malignancies. Renal complications occur rather rarely compared to multiple myeloma. The most common renal manifestations are mild proteinuria and microhematuria. We describe a case of MW presenting with acute renal failure and NS. A 67-year-old man was referred to our hospital for sudden onset nephrotic syndrome. Electrophoresis revealed a monoclonal component in the gamma region, which was classified as an IgM k. During hospitalization, acute kidney injury developed, with creatinine up to 5 mg/dL, despite adequate hydration and alkalinization. A kidney biopsy was performed, showing minimal change disease (MCD) with interstitial and capsular lymphoid infiltrates of B-Lymphocytes CD20+. B-lymphocytes infiltration suggested the possibility of renal localization of lymphoproliferative disorder. So, bone marrow histology was performed, revealing lymphoplasmacytic lymphoma (WM). The patient was treated with bortezomib, desamethasone, and rituximab, with partial recovery of renal function (creatinine 1.5 mg/dL) and complete remission of proteinuria after 8-month follow-up. The remission of NS in our patient with rituximab seems to emphasize the pathogenetic role of B cells in MCD, although a coincident effect of immunosuppression on both the underlying renal disease and the hematologic disease cannot be excluded.