Objective: Hypothalamic hamartomas (HH) constitute rare developmental lesions associated with gelastic seizure, precocious puberty, and abnormal behavior. Treatment for this lesion is very complicated due to its location. Gamma Knife radiosurgery (GKS) may be an efficient and safe treatment option, which produces little morbidity. The authors evaluated the long-term results of GKS for the HH. Methods: Eights patients with HH-related intractable gelastic seizure and/or precocious puberty underwent GKS between 1992 and 1996, with a mean age of 8.3 years at the time of GKS (range, 3.5-17.7 years). Three patients were presented with intractable gelastic seizure, and 4 patients with precocious puberty. One patient had both intractable seizure and precocious puberty. The mean follow-up duration was 76.6 (28.9-141) months. Results: The mean marginal dose for the large sessile type HH with intractable gelastic seizure was 11.5Gy (range, 9-13Gy) and that for the small pedunculated type with precocious puberty was 27Gy (range, 20-34Gy). There was no lesion volume change on follow-up MRI. Intractable seizure disappeared in only 1 patient and was not improved in the other 3 patients. Precocious puberty was not resolved by GKS in all cases. Conclusion: The long-term results of GKS for HH were not satisfactory. As for the control of epilepsy, the radiation dose in our cases was not enough to suppress and block the epileptogenic focus of HH and its propagation to surrounding tissue. Precocious puberty caused by HH is not indicated for GKS. If we could get better treatment outcome with higher radiation dose and/ or new dose planning technique, GKS might be primary treatment option for HH.