The effect of gamma knife radiosurgery for cranial base meningiomas was analyzed using magnetic resonance (MR) imaging in 33 patients followed up for a mean 26.5 months. There were 10 male and 23 female patients aged from 38 to 87 years (mean 54.5 yrs). Twenty-three patients had already had more than one open surgery before radiosurgery. The mean tumor volume was 16.8 cm³. The mean maximum dose was 29 Gy and the mean marginal dose was 15.1 Gy. Four patients were treated by two-stage treatment at 1 to 4-month intervals. Follow-up MR imaging revealed a decrease in tumor size in 10 patients, a small low intensity area in the tumor center in three, increase in tumor size in two, and no change in 18. After radiosurgery one patient had marked edema on MR imaging and showed cognitive deficits, and another three patients had neurological deterioration. All other patients were unchanged or improved. Growth control of cranial base meningiomas without severe neurological deficits can be achieved by radiosurgery.