OBJECTIVE: The results of gamma knife radiosurgery(GKRS) for growth hormone(GH)-secreting pituitary adenoma are investigated to identify the role of adjuvant GKRS for remnant or recurrent tumor following transsphenoidal approach(TSA). METHODS: From March 1992 to December 2001, 20 patients treated by GKRS for GH-secreting pituitary adenoma following TSA were followed up more than 3 years and evaluated their symptomatic, hormonal and radiological changes after radiosurgery. RESULTS: There were 6 men and 14 women and the mean age was 40.2 years (range 24-58 years). The maximal dose was 32 to 60Gy (mean 46.2Gy) and the marginal dose was 12.8 to 36Gy (mean 25.5Gy). The mean follow-up time was 5.9 years (range 3-10years). Normalization of GH level (below 2ng/ml) was achieved in 10 of 20 patients (50.0%), and the normalization of IGF-I was in 8 of 15 patients (53.3%). On follow up MR imaging, the tumor control rate was 100% and the tumor volume reduction rate was 25~50% in 4 patients, 50~75% in 13 patients and 75~100% in 3 patients. CONCLUSION: In the treatment of GH-secreting pituitary adenoma, tumor control rate and improvement of clinical symptom show good outcome without major complication after adjuvant GKRS following TSA, though the rate of normalization of GH level is unsatisfactory. The optimal marginal dose for GH-secreting pituitary adenoma is more than 25Gy, and secondary GKRS can be considered in the failed cases to achieve effective hormonal normalization after the first adjuvant GKRS.