A 52 year old man was admitted to hospital for persistent back pain, fixed proteinuria of 6g/24 h that lead to the nephrotic syndrome (proteids 40 g/l, albumin 21,2 g/l). Two possible etiologies were envisaged: 1) Myeloma with K light chains as evidenced by biological findings (absence of normal Ig, presence of K light chains both in blood and urine, malignant medullary plasmocytosis) as well as x-rays (small punched out lesions). 2. Diabetes mellitus (blood glucose 2,4 g/l) with retinal and neurological involvement. Percutaneous renal biopsy revealed nodular glomerular sclerosis compatible with both diabetes and myeloma as well as homogeneous refringent thickening of tubular basement membranes more specific of myloma. No amyloid deposits, myelomatous casts were seen and anti-K light chain fixation was negative at immunofluorescence. An evolution of 33 months duration let to chronic renal failure (plasma creatinine 47 mg/l). The respective role of myeloma and diabetes in the genesis of this glomerular nephropathy are discussed.