'Benign' aqueduct stenosis is a common cause of hydrocephalus in the paediatric population and is frequently treated by endoscopic third ventriculostomy. Occasionally, aqueduct stenosis can be a prelude to the development of other pathology, as is seen in these two cases of pineal tumours developing in patients whose hydrocephalus was successfully treated with endoscopic third ventriculostomy. The case histories are presented, along with the recommendation for increased radiological screening of patients with this usually 'benign' presentation.