Six patients are with inappropriate secretion of antidiuretic hormone syndrome are reported (two with bacterial acute meningitis, two with bacterial pneumonia, one with oat cell lung carcinoma, other with mediterranean fever boutonneuse) and the clinical manifestations were: mind changes (four cases) nausea-vomiting (two cases) and inappetence (six cases). All patients presented hyponatremia criteria, serum decreased osmolarity, urinary sodium and osmolarity increased, without edemas, renal disease endocrine (hypophysis, thyroids, adrenal) without diuretic treatment. Treatment was, effective water restriction in three patients and hydrochloride of demeclocycline in other three patients.