A 67-year-old man, on oral therapy for type 2 diabetes mellitus since 1990, had sustained proteinuria since 2005. When hematuria was first discovered in 2008, renal dysfunction [creatinine (Cr), 1.2 mg/dL], inflammation [C-reactive protein (CRP), 12 mg/dL] and high myeloperoxidase anti-neutrophil cytoplasmic antibodies (MPO-ANCA) levels [546 ELISA units (EU)] were observed. Renal biopsy showed the diagnosis of ANCA-associated nephritis combined with diabetic nephropathy. For this patient, there was pathological proof of the combination of diabetic nephropathy and ANCA-associated vasculitis.