We report a case of multiple myeloma that presented with anorexia, fatigue, high erythrocyte sedimentation rate, bone marrow plasmacytosis of more than 30%, polyuria,and low urine specific gravity. This unusual presentation was diagnosed as nephrogenic diabetes insipidus secondary to a proximal tubular dysfunction. The tubular functional disturbance appeared to be related to the presence of lambda-type light chains. The patient was treated with desmopressine without response. After one month of treatment with thalidomide and dexamethasone for myeloma there was a dramatic response with decreased urine output.