Objective: The purpose of this study is to assess the efficacy and advantages of an endoscopic endonasal approach for the treatment of pituitary tumors. Methods: We retrospectively analyzed the records of 31 patients with pituitary tumors having endoscopic endonasal surgery between March 1999 and August 2003. Results: Among 31 patients with pituitary adenomas, 25 (81%) patients exhibited gross total removal of tumor on postoperative MRI within 3 days after surgery. Among 6 patients removed subtotally, 2 had only radiosurgery, 3 have had periodic follow-up MRIs and one patient with large extended tumor (grade IV, Stage E) had secondary transcranial removal of tumor before radiosurgery. Postoperative complications included cerebrospinal fluid leak in 2 patients, sinusitis in 1 patient, and one patient died due to unexpected intracerebral hemorrhage on 5 days after surgery. Besides considerable experiences with this approach are needed because of narrow working channel to the sella turcica, the results of our study showed following advantages of this procedure: visualization of areas not seen with the operating microscope, elimination of oronasal complications, more functional and cosmetic outcome, and shortened operative time and hospital stay. Conclusion: The authors consider that endoscopic endonasal transsphenoidal approach provides good results with minimal invasion for patients with pituitary tumors.