Hyponatremia is the most frequent electrolyte disorder of hospitalized patients and is associated with a longer hospital stay and serious symptoms. The syndromes of inappropriate antidiuretic hormone secretion (SIADH) and cerebral salt wasting (CSW) are 2 potential causes of hyponatremia in patients with disorders of the central nervous system. In both syndromes, serum osmolality and plasma uric acid are decreased; blood antidiuretic hormone and urine sodium levels are increased; and plasma albumin concentration and plasma K+ levels are normal. This case report highlights the link between lightning-induced brain injury and CSW syndrome. A 16-year-old boy was admitted to our emergency department because of lightning injury and was unconscious. His Glasgow Coma Scale score was 13. Second-degree burns at the left knee and ankle, at the right leg, and at the occipitoparietal region with a 3-cm area of singed hair were noted. On the second day, the examination showed dry mucous membranes and slightly decreased skin turgidity. He had normal blood pressure throughout hospitalization, and excessive urine output was noted. A decrease in body weight (maximum of 0.450 kg) was observed. Biochemical examination found a rapid drop in serum sodium levels after admission. The diagnosis of central hyponatremia and CSW in the context of lightning injury was made owing to negative salt and water balance. Hypertonic saline solution was given. The patient was discharged home on the fifth day of hospitalization with normal serum chemistries and without the need for sodium supplementation.