BACKGROUND: Microsurgical free tissue transfer has become a reliable technique. Nevertheless, 5 to 25 percent of transferred flaps require re-exploration due to circulatory compromise. This study was conducted to evaluate the timing of occurrence of flap compromise following free tissue transfer, and its correlation with salvage outcome. METHODS: Between January of 2002 and June of 2003, 1142 free flap procedures were performed and 113 flaps (9.9 percent) received re-exploration due to compromise. All patients were cared for in the microsurgical intensive care unit for 5 days. Through a retrospective review, timing of presentation of compromise was identified and correlated with salvage outcome. RESULTS: Seventy-two flaps (63.7 percent) were completely salvaged and 23 (20.4 percent) were partially salvaged. Eighteen flaps (15.9 percent) failed completely. Ninety-three flaps (82.3 percent) presented with circulatory compromise within 24 hours; 108 (95.6 percent) presented with circulatory compromise within 72 hours, and 92 flaps (85.2 percent) were salvaged within this period. One out of the three flaps presenting with compromise 1 week postoperatively was salvaged. Flaps presenting with compromise upon admission to the microsurgical intensive care unit had significantly lower complete salvage rates as compared with those without immediate abnormal signs (40.9 percent versus 69.2 percent, p = 0.01). CONCLUSIONS: The time of presentation of flap compromise is a significant predictor of flap salvage outcome. Intensive flap monitoring at a special microsurgical intensive care unit by well-trained nurses and surgeons allows for early detection of vascular compromise, which leads to better outcomes.