A case of multiple myeloma with severe osteolytic destructions and myeloma kidney is presented, in whom a rapidly progressive renal insufficiency because of hyponatraemia and dehydration developed. After 5 months of regular dialysis treatment diuresis increased and a sufficient global kidney function recurred. Aetiological factors and the pathomechanisms of acute renal failure in multiple myeloma are discussed. We assume that acute renal insufficiency is - in rare cases - at least partly reversible. Therefore patients with acute renal failure and multiple myeloma should not be excluded from haemodialysis treatment because even complete rehabilitation can be achieved.