Children with brain tumors routinely undergo craniotomies for tumor resections. Nurses and nurse practitioners are critical in closely monitoring these patients. Postoperatively, these children may develop inappropriate vasopressin secretion, cerebral salt wasting syndrome, or a combination of both. Inappropriate fluid and electrolyte administration may exacerbate symptoms. Both high and low sodium levels are associated with significant complications. Sodium levels were prospectively observed for 72 hours perioperatively. Overall, 36 patients had 201 serum sodium levels measured over the course of 1 year. Postoperatively, 79 (39%) of the sodium levels were <135 mEq/L or >145 mEq/L. Of these abnormal sodium levels, 3 (1%) were <125 mEq/L and 2 (1%) were >165 mEq/L. All the abnormal sodium levels occurred in patients with suprasellar or hypothalamic lesions. This study suggests that children with resections of suprasellar or hypothalamic tumors need specialist attention in postoperative management of fluid and electrolytes. The nurse is in the ideal role to monitor closely the pediatric brain tumor patient at high risk for abnormal sodium levels.