<i>Background/Aims:</i> It is not exactly known how many children develop the triphasic response (diabetes insipidus (DI)/hyponatremia/DI) immediately after surgery for childhood craniopharyngioma; neither is it known which factors predict this. We studied the occurrence of the triphasic response after primary surgery for craniopharyngioma in children, and aimed to identify possible predictors. <i>Methods:</i> Patients <18 years old who had undergone a primary craniopharyngioma resection between January 1990 and February 2010 in either of the 2 academic centers in Amsterdam were studied retrospectively. <i>Results:</i> Twenty-one patients (5 males) fulfilled the inclusion criteria. Median age at surgery was 9.1 (range: 4.0–15.1) years. Six patients developed a triphasic response (29%). Of all factors, only the duration of surgery was found to be a predictor of a triphasic response: 8.5 (6.0–11.0) versus 4.6 (3.5–11.5) h in patients who did not develop a triphasic response (p = 0.03). <i>Conclusion:</i> After primary surgery for a craniopharyngioma, a considerable number of patients develop a triphasic response in the regulation of the sodium and water balance. This is predicted by (factors associated with) a longer duration of surgery. Other predictors could not be identified, which may be due to the small sample size.