25 patients with low-flow carotid-cavernous fistula (CCF) underwent radiosurgery between 1977 and 1992. 22 had spontaneous low flow fistulae and 3 traumatic high flow fistulae which had been previously treated with internal carotid trapping. The mean preoperative symptomatic period was 12.2 months (4-24 months). Fistulae were classified according to Barrow's classification. Type T was added for traumatic, high-flow fistulae with flow reduction after internal carotid trapping. 11 cases were of type B, 4 of type C, 7 of type D and 3 of type T. The target point for radiosurgery was calculated from selective internal or external carotid angiograms. Stereotactic radiosurgery was performed with a cobalt source, with 5- to 10-mm collimators. A total dose of 30-40 Gy was delivered in all cases, except 1 posttraumatic case in which the dose was 20 Gy. The follow-up period ranged between 14 years and 15 months (mean: 49.76 months). 20 of the 22 low flow fistulae (90.9%) completely closed in a mean period of 7.5 months (range: 2-20 months) after radiosurgery. Improvement of the symptoms began at a mean period of 2.37 months (range: 0.5-14 months). There were no recurrences, the follow-up period ranging between 14 years and 15 months. 100% of type B CCF closed after a mean period of 5.9 months, 75% of type C closed after a mean period of 12.66 months, and 85.7% of cases of type D closed after a mean period of 8.16 months.(ABSTRACT TRUNCATED AT 250 WORDS)