The syndrome of inappropriate ADH secretion is a disorder characterized by hyponatremia which results from water retention attributable to ADH release. The hallmark of SIADH is hyponatremia due to water retention, in the presence of urinary osmolality above plasma osmolality. The SIADH was initially described by Schwartz et al(1957). This syndrome, first recoginzed in patients with bronchogenic carcinoma, has now been observed in a variety of other illnesses. Recently, we encountered a 59 year-old female with small cell lung cancer, also she had SIADH. Thus, we present a case and review the literature on the subject.