Stereotactic radiosurgery has been an important treatment modality in the treatment of pituitary adenomas. However, it has the disadvantage of a delayed effect on hormonal normalization compared with microsurgical resection of functioning pituitary adenomas. To define the efficacy of radiosurgery in the treatment of functioning pituitary adenomas, 37 cases with a mean follow-up duration of 26.9 months were analyzed. There were 18 prolactinomas, 11 cases with acromegaly, and 8 cases with Cushing s disease. The mean maximum dose was 54.8 Gy. The tumor margin was encompassed within the 50 to 90% isodose. The level of serum prolactin, growth hormone, and 24-hour urine free cortisol were evaluated for hormonal follow-up according to the relevant endocrinopathy. There was 35.1% hormonal normalization and an 81.8% decline in hormone levels to below 50% of the preoperative value (hormonal response). Hormonal normalization was obtained in 13 patients (mean latency = 22 months). A hormonal response was seen in 30 patients (mean latency = 7.6 months). The maximum dose and tumor volume included in the prescription isodose were significantly correlated with the latency period from radiosurgery to hormonal normalization. These results suggest that early hormonal normalization can best be achieved by a high maximum dose (at least 55 Gy) and broad coverage of the target tumor volume within the prescription dose thereby increasing the integral dose.