Radiosurgical treatment of pituitary and peri-sellar tumors has become an increasingly utilized modality as an alternative to conventional radiotherapy and surgery. Such radiosurgery results in a relatively high dose of radiation to the optic chiasm. The clinical data establishing safe single-fraction doses to the chiasm is immature, although taken together previous literature suggests a recommended maximal dose of 8 Gy. Optic neuropathy, when it occurs, tends to take place within 2 years of treatment. We evaluated the visual fields of 20 sequential patients that received significant doses to the optic chiasm by Gamma-knife radiosurgery. There were 17 cases of pituitary adenoma and 3 cases of meningioma, and two patients refused follow-up testing. Preoperative visual field and cranial nerve examinations were done prior to radiosurgery and in follow-up, with a median follow-up of 24 months. There were no cases of quantitative visual field deficit induced by treatment. No patients developed symptomatic visual deterioration. Radiat. Oncol. Invest. 90:343-350, 2000. 2000 Wiley-Liss, Inc.