A 59 year old man presenting fever, serum hyponatremia and hypoosmolality in association with hyperosmotic urine was hospitalized in our unit in February 1988. We demonstrated evidence of systemic sarcoidosis and inappropriate secretion of antidiuretic hormone (ADH). The patient was treated with corticosteroid therapy for a period of about 1 year, with regression of signs of the inappropriate vasopressin secretion as well as the symptomatology related to systemic sarcoidosis. This study identified systemic sarcoidosis as a definite cause of "syndrome of inappropriate ADH secretion".