We describe a case of severe hyponatremia following chemotherapy administration in a patient with small-cell lung cancer. There was no evidence of the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. The clinical and laboratory findings were consistent with a sodium-wasting nephropathy complicating cisplatin administration. There are few well-documented reports of cisplatin-associated hyponatremia in the medical literature. We have summarized the relevant literature and attempted to define the differential diagnosis of hyponatremia in this setting. Most cases are accounted for by sodium-losing nephropathy of SIADH, but many reported cases contain insufficient data for classification. Appropriate attention to the evaluation of hyponatremia following platinum-based chemotherapy is needed to properly treat these conditions.