OBJECTIVE Evaluation of outcome and prognostic factors in patients with brain stem glioma (BSG) following fractionated stereotactic radiotherapy (FSRT). METHODS Between 1990 and 1997, we treated 41 patients with FSRT in a phase I/II trial. Median age was 24 years. Out of 36 patients with histologically proven glioma, ten had a partial tumour resection. Histology revealed low grade gliomas in 30 patients and anaplastic gliomas in six patients. A mean total dose of 54 Gy was given in daily fractions of 1.8 Gy. Median follow-up was 12 months. RESULTS Three patients died during FSRT. Neurological improvement was achieved in 19/38 patients. Reduction of tumour size was reported in 12/38, in 16 patients the lesion was unchanged, ten showed progression. Median time to progression was 23 months, median overall survival 40 months with an actuarial survival of 83% at 1 year, 55% at 3 years and 33% at 5 years. In 20 of 22 patients with recurrence progression was inside the target volume. Significant prognostic factors for survival were clinical and radiological response 6 weeks after FSRT. Treatment toxicity was mild. Ototoxicity occurred in one patient. CONCLUSIONS FSRT is a feasible treatment modality for BSG with tolerable toxicity. The risk of marginal failure is low.