Arteriovenous fistulae are abnormal communications between arteries and veins, leading to bypass of the normal capillary bed circulation, often with progressive enlargement giving rise to multiple complications. The occurrence of the arteriovenous fistula after a microsurgical operation is a rare complication. Hurst and Sukop have reported the occurrence of arteriovenous fistulae following replantation surgery; Collin has reported an arteriovenous fistula arising in a free flap in head and neck surgery. There are no published accounts of the arteriovenous fistula arising in free flaps in hand surgery. In this article, we present the case report of a patient with a spontaneous arteriovenous fistula followed by free transfer of an anterolateral thigh flap, a rare complication in free flap surgery.