Flap failure in free-tissue transfer relates strongly to technical failure of the anastomosis or to kinking as well as to external compression of the donor or recipient vessels. Intraoperative monitoring of flap perfusion has shown to prevent flap failure. This prospective, clinical study presents the results of intraoperative dynamic infrared thermography as a novel method to monitor reperfusion indirectly in 10 free flaps. This noninvasive technique provided a fast and reliable method to register partial or total arterial occlusion due to anastomotic failure, as well as due to external compression or kinking of the vessels. The dynamic infrared image sequences showed an improved rate and pattern of rewarming of the flap after an additional venous anastomosis was opened. The state of reperfusion of the flap at the end of the operation could easily be determined. The authors conclude that dynamic infrared thermography provides the surgeon with valuable information on flap reperfusion during free flap surgery.