Objectives : Stereotactic radiosurgery using gamma-knife in adjunct to transsphenoidal pituitary surgery is recently being used for treatment of pituitary adenomas and it poses as an effective and safe treatment modality. We present our experience and preliminary results of gamma-knife treatment of the patients with pituitary adenomas. Methods: Between May, 1992 and March, 1994, 20 patients with pituitary adenoma were treated with gamma-knife at Yonsei Medical Center. Among them, 15 cases who have had follow-up for more than 6 months were included in our study. 13 of 15 cases had endocrinologically active tumors(4 prolactin secreting, 4GH secreting, 5 ACTH secreting), and two patients had clinically non-functioning adenomas. Hormonal and radiological studies and clinical features were followed up. Results: After gamma-knife surgery, the hormonal level was decreased in eleven of thirteen patients with functioning pituitary adenomas and the size of tumor was decreased in seven of fifteen patients and eleven of fifteen patients were improved clinically. There was more favorable results in Cushing's disease than in other pituitary adenomas. There was no severe complication associated with gamma-knife surgery, Conclusion : Based on our initial clinical experience, we believe that gamma-knife stereotactic radio surgery is safe and effective alternative to conventional neurosurgery in selected patients with pituitary adenomas and further study might be warranted.