Objective   To investigate the treatment effect of gamma knife radiosurgery for hypothalamic hamartomas.     Methods   Gamma knife radiosurgery was performed in 9 patients with gelastic seizures. Collimator helmets (4 and 8 mm) were used and a radiosurgery plan was designed to cover 90% of the hamartoma at the 40%~55% isodose curve with the center dose of 28~40 Gy and the margin dose of 12~18 Gy. The clinical outcome was evaluated with the Tan’s scale.     Results   No complications due to gamma knife radiosurgery occurred. A follow-up from 24 to 54 months showed effectiveness in 7 patients

disappearance of seizure in 1 patient

rare occurrence in 3 patients

significantly reduced occurrence in 2 patients

improvement in seizure control in 1 patient

but ineffectiveness in 2 patients.     Conclusion   As an approach to the treatment of hypothalamic hamartomas

gamma knife is a safe and cost-effective therapy with rare side effects for hypothalamic harmatomas.