OBJECTIVE: This study is designed to assess the cause of post-treatment bleeding after gamma knife radiosurgery(GKRS) for cerebral arteriovenous malformation(AVM). METHODS: We experienced post-treatment bleeding in seven cases out of 214 AVM patients group before complete obliteration and analyzed their clinical characteristics, angiographic architecture and radiosurgical dosimetry. RESULTS: Hemorrhage rate was 3.2% (7/214) and the bleeding occurred individually at 4, 8, 9, 20, 44, 44 and 115 months after GKRS. Annual bleeding rate was 0.6% (7 episodes of bleeding / 1131 patient years). Three patients presented with hemorrhage as initial symptom upon admission and four patients were admitted with other symptom rather than hemorrhage. AVM was deep-seated in 4 cases, and at motor cortex in three patients. Average marginal dose was 18.9Gy (range;10-25Gy). Most of patients showed angiographic risk factor for bleeding such as venous aneurysm, multiple venous drainage, dual arterial supply and shunt type. Upon bleeding incidence, emergency operation was performed in 5 cases and two patients received second GKRS. Two patients were expired after emergency operation. CONCLUSION: The risk of hemorrhage from GKRS for AVMs is inevitable, even if patients are in non-hemorrhagic group before complete obliteration. In order to minimize hemorrhage rate, intensive follow-up is strongly suggested after radiosurgery, and the retreatment for a residual nidus is recommended at early point after the latency period.