One-hundred and fifty consecutive free-tissue transfers were reviewed to evaluate the role of emergent exploration in flap survival. Eleven flaps exhibited signs of circulatory failure between 1 hour and 6 days postoperatively and required return to the operating room. In eight patients the preoperative diagnosis was venous thrombosis, and in three patients it was arterial thrombosis. The average time from the first abnormal examination to exploration was 1.5 hours. There were no false-positive explorations. All 11 flaps were salvaged following correction of the cause of circulatory compromise. In eight patients this was due to inflow or outflow obstruction in the recipient vessels proximal to the anastomosis, in two patients it was due to extrinsic compression of the flap from a tight wound closure, and in one patient it was due to obstruction of the recipient vein by a drain. Primary anastomotic thrombosis was not encountered as the cause of circulatory compromise in any patient. An aggressive approach to exploration was responsible for an increase in flap survival in the entire series from 90 to 98 percent. The results of this study demonstrate the efficacy of clinical monitoring, the role of early exploration, and the durability of microvascular anastomoses.