Antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3) have been demonstrated to mediate anti-neutrophil cytoplasmic antibody (ANCA)-associated disease. For membranous nephropathy, antibodies to the podocyte-expressed phospholipase A(2) receptor (anti-PLA(2)R) are highly associated with disease activity and have been reported in at least 70% of patients with idiopathic membranous nephropathy (IMN). We present a case of a 56-year-old male with a 1 year history of hypertension, leg edema, and proteinuria, who presented with advanced renal failure and was found to have both ANCA-associated glomerulonephritis (GN) and IMN on kidney biopsy. Consistent with the idea that this is due to the chance occurrence of two independent diseases, we found both anti-MPO and anti-PLA(2)R antibodies in the patient's sera. Treatment with methylprednisolone, plasmapheresis, and cyclophosphamide resulted in improvement in kidney function and proteinuria, together with the simultaneous decrease in both autoantibodies. This is the first demonstration of two pathogenic antibodies giving rise to ANCA-associated GN and IMN in the same patient. It confirms the importance of classifying disease based upon the underlying mechanism, in addition to renal histopathology, to both optimize therapy and predict prognosis.