This study reports on a 67-year-old man, suffering from type 2 diabetes mellitus for 11 years along with arterial hypertension and autoimmune thyroiditis, in whom nephrotic proteinuria was detected together with a mild reduction in GFR. No autoantibodies or monoclonal proteins were detected in blood and urine. Renal biopsy material examined by light microscopy, immunofluorescence and electron microscopy showed AL amyloidosis. This case underlines the role of renal biopsy in patients with type 2 diabetes mellitus, in whom renal diseases other than diabetic nephropathy may occur frequently.