We report the first case series of 14 children with intracranial germ cell tumour (iGCT) and concomitant central diabetes insipidus (DI), who developed hyponatremia secondary to renal salt wasting syndrome (RSWS) following the administration of carboplatin. Clinicians prescribing platinum-based chemotherapy for this group of patients should be alert to the risk of RSWS. Regular monitoring should be performed as hyponatraemia can be asymptomatic until it is severe.