Although the occurrence of CSF oedema and cyst has been described in presence of a blocked ventriculoperitoneal shunt, especially distal end block, its occurrence in presence of a well functioning shunt has not been described so far. We report a case where a 51-year old lady developed an insidious onset and gradually progressive CSF cyst without any clinical or radiological feature of shunt block over a period of about 2 years. The changes started about 6 months after a course of radiation therapy for an extensive residual supra and infratentorial meningioma. Following surgery, where the cyst was punctured and a new ventricular catheter was inserted, despite well functioning upper and lower end, the cyst gradually disappeared. We review the literature and hypothesize that the radiation-induced changes were responsible for initiation and progression of the cyst.