The risk for free flap thrombosis is greatly influenced by blood flow. Postoperative hemodynamic changes in vascular pedicles of the microvascular skin flap have not been reported, however. This study focuses on the intraoperative and postoperative changes in the flow volume in the vascular pedicles of the free forearm flap examined by color Doppler ultrasonography. The arterial flow volume increased continuously until day 7, compared with which, the volume after flap elevation was 36%. On day 1, it reached only 52%. In the venous pedicle, the flow volume through the cutaneous vein was only 37% compared with that through the radial vena comitans after flap elevation, whereas the volume through both veins was equal on day 7. Drastic changes in the flow explain the possible vascular occlusion during the early postoperative period in the free forearm flap transfer.