Six consecutively presenting patients with craniopharyngiomas, (F:M = 4.2; mean age: 35.2 years, range 17-58) histologically proven by one or more previous operations, and with recurrence of a wholly or predominantly cystic nature, were treated by 90yttrium (90Y) radioisotope instillation into the cyst. Five patients had undergone external beam radiotherapy and the remaining patient had concomitant stereotactic radiosurgery to a co-existing solid component. Seven cysts in six patients have been treated. Five cysts, previously requiring repeated aspiration at intervals of 2-20 weeks have required no further surgical intervention following 90Y treatment (FU mean 3.5 years, range 1.2-7), although two of these required a second 90Y treatment. No patient developed a visual field defect or evidence of hypothalamic dysfunction. One patient died within a month of treatment from complications related to a solid recurrence. One patient developed a large solid/cystic recurrence at 4 months and died shortly thereafter from an unrelated cause. We summarize results from other series that have demonstrated the efficacy of this technique, usually as primary therapy, but this is the first series to demonstrate its usefulness as salvage therapy. The prospect of survival with good quality of life can be offered to patients with multiply recurrent disease who have exhausted all conventional means of treatment. In our experience intracavitary 90Y is a safe and highly effective means of controlling cystic recurrence in refractory craniopharyngioma. Some patients require more than one treatment.