PURPOSE: Autologous fat injection is ideal for patients who wish to add contour, projection and gross volumization of the aging, atrophic face and is claimed to be a safe procedure. However, there are several case reports in the literature where patients have suffered from acute visual loss and cerebral infarction after facial fat injection. This paper explores a rare case of vessel related complication, an arteriovenous fistula that occurs after fat injection on forehead. METHODS: A 28-year-old female who showed a non- tender, soft 1.0x2.5cm sized mass on forehead for 3 weeks. A thrill could be detected on the tortuous dilatated vessel-like structure around the mass. She had a fat injection on forehead for soft tissue augmentation 3 months prior to developing the mass. 3-dimensional brain CT angiography showed arteriovenous fistula. RESULTS: The fistula is totally excised with ligation of feeding vessels. Pathology report showed an atypical vessel which had intimal thickening, myxoid degeneration and thrombus formation. There were no evidences of recurrence at least for 2 months of follow-up. CONCLUSION: An occurrence of arteriovenous fistula after autologous fat injection is very rare. After perforation of artery and vein by coincidence, blood extravasates with the formation of a hematoma capsule and a pseudocapsule around it. The hematoma capsule would expand and clot would reabsorb resulting in a cavity leading to fistula formation. Other vessel related complications like acute visual loss or cerebral infarction are very severe. Therefore, surgeons should be cautious during facial fat injection to avoid vessel injuries.