Malignant lymphomas can affect kidneys in several ways. They may precipitate acute renal failure by causing ureteral or renal vascular obstruction, or by direct renal parenchymal infiltration. Furthermore, they may insult renal function via paraneoplastic mechanisms such as hypercalcemia. Lymphomas only rarely can cause glomerulonephritis (GN). We report a case of a 72-year-old male who presented with mild renal function impairment, proteinuria, and microscopic hematuria, suggesting active glomerulonephritis, and pancytopenia of immune origin. A bone marrow biopsy led to a diagnosis of splenic marginal zone lymphoma. Although a kidney biopsy was not performed, glomerulonephritis was attributed to the lymphoma and splenic marginal zone lymphoma-related glomerulonephritis was the final diagnosis. The course of splenic marginal zone lymphoma is extremely indolent. The first manifestation in some patients can be immune cytopenia or other autoimmune phenomena. These patients may respond well to corticosteroids. Therefore, our patient was started on prednisolone resulting in a good hematologic response. Renal function also improved and proteinuria and hematuria disappeared, suggesting a lymphoma-related origin of the GN. Two years after full steroids withdrawal, the patient remained stable with a good renal function and daily protein excretion less than 300 mg. Lymphomas rarely are the cause of secondary glomerulonephritis; however, with a lack of an apparent cause, the clinician should be aware of them, particularly in the elderly with autoimmune manifestations.