Background: Pilocytic astrocytoma is one of the commonest subtypes of glioma to affect children. However, they are rarely diagnosed in patients over the age of 18 years. In adults, these tumours appear more frequently supra-tentorially than in the cerebellum and some reports suggest a different clinical course in adults. We reviewed ten patients aged 18 or over who had been operated on for cerebellar pilocytic astrocytoma to assess the impact of tumour biology and extent of resection on outcome in adults. Method: Patients were identified from a neuropathology database and a retrospective chart review of ten patients was performed. Recorded data included patient demographics, tumour location, presenting features, radiological appearance, extent of surgical resection, tumour recurrence and Ki-67 proliferation index. Results: Nine patients were men and one patient was a woman. Median follow up is 41.5 months (range 15-334 months). Complete surgical resection was achieved in nine of the patients operated in our institution. One patient had prior subtotal resection elsewhere. Tumour recurrence was seen only in the two patients with subtotal resection, at 7 and 25 years. Ki-67 ranged from <1 to 10 % and appears to have no correlation to recurrence. No patients in this series had adjuvant treatment. Conclusions: Cerebellar pilocytic astrocytomas in adults should be treated with macroscopic complete surgical resection whenever possible. If this is achieved, long-term survival rates are excellent, whereas subtotal resection carries a high risk of tumour recurrence. Ki-67 is less important prognostically than the extent of initial resection. [ABSTRACT FROM AUTHOR]