A 78 year old white male on methimazole due to Grave's thyroiditis presented with acute renal failure after a short term history of progressive shortness of breath, malaise, myalgias, arthralgias, and bilateral lower limb swelling. The abdomen was remarkable for splenomegaly and lower extremities for erythema nodosum. No peripheral lymphadenopathy was detected. Serum albumin was 1.7 g/dl and very high erythrocyte sedimentation rate. Urine sediment was very active with dysmorphic red blood cells and casts and significant proteinuria (6.6 grams/day). Serum complements were abnormally low and antinuclear and anti-DNA antibodies were positive. Renal histopathology revealed membranoproliferative glomerulonephritis, along with a full house pattern on IFF consistent with lupus nephritis. Bone marrow aspiration revealed a 40% infiltration by a lymphocyte population of small cells consistent with a B cell non-Hodgkin lymphoma. The patient was treated with methylprednisolone, cyclophosphamide and rituximab and acute dialysis. Over the following weeks the patient became dialysis independent and returned to his baseline GFR.