In the period of 6 years (1992-1998) we treated 26 patients with brain stem cavernomas using the Leksell gamma knife at the Hospital Na Homolce. 25 patients had a follow up of 6 - 51, median 24 months. The annual risk of haemorrhage before radiosurgery was 4%. After gamma knife radiosur- gery sudden impairment of neurodeficit assigned as rebleeding was observed in 4 patients 6 - 51, median 16.5 months after radiosurgery. This represented 7.6% risk of rebleeding after radiosurgery. MRI or CT was performed in 24 patients 6 - 48, median 21 months after radiosurgery. There were no signs of rebleeding in any of the patients, nor enlargement of the cavernoma. A diminution of the cavernoma was observed in 8 (33%) patients. Collateral oedema after radiosurgery was detected in 5 (21%) patients 3 - 12, median 11 months after radiosurgery. Neurodeficit was observed in 21 patients before radiosurgery. Improvement of neurodeficit was detected in 9 (43%) of them 6 - 36, median 8 months after radiosurgery. Temporary morbidity caused by collateral oedema or rebleeding was 24% and permanent morbidity was 8%. 2 patients died because of rebleeding 6 and 51 months after radiosurgery. Radiosurgery of brain stem cavernomas is indicated when there was overt bleeding in the history or progressive neurodeficit and microsurgery is considered too risky. Leksell gamma knife radio- surgery of cavernomas proved its low morbidity and zero mortality. In case of insufficient effect of radiosurgery, or if the protective effect from rebleeding comes too late, mortality can correspond to the risk of the natural course of the disease, as if left without treatment.

        Key words: cavernoma - angiographically occult vascular malformation - radiosurgery - gamma knife - therapy - result