PURPOSE: Diabetes insipidus(DI) has been known to be a relatively common complication after craniotomy. We have investigated the incidence and clinical course of DI in children related to craniotomy for a brain tumor and determined the risk factors of postoperative DI. METHODS: Sixty-two pediatric patients, who have undergone craniotomy for a brain tumor(including stereotactic biopsy) from February 1995 through January 1998, were included in this study. We reviewed hospital records retrospectively and analyzed daily fluid intake and output, electrolytes and osmolarity of serum and urine, and urine specific gravity. RESULTS: Of 62 patients, DI developed preoperatively in 7 patients and postoperatively in 7 patients. Preoperative DI composed of 4 germinoma, 2 craniopharyngioma and a histiocytosis, followed by permanent DI after operation. All of the postoperative DI were composed of suprasellar tumors, including 4 craniopharyngioma, which progressed to permanent DI in 5 cases and transient DI in 2 cases. The 5 patients had a triphasic response. The initial phase of DI began within 12 hours postoperatively followed by antidiuretic phase at the 2nd-6th postoperative day, lasted 1-6 days and finally all patients entered permanent DI. Hypopituitarism developed in 10 patients and all of them were accompanied by permanent DI. CONCLUSION: DI is a common complication after neurosurgery for the hypothalamic or pituitary area. The high-risk factors of permanant DI are preoperative DI, combined hypopituitarism or triphasic response. Therefore, it is important to closely monitor this high-risk group, and we should consider endocrinological evaluation in patients who had undergone craniotomy for a brain tumor.