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The aim of this study was to evaluate perioperative flap perfusion using noninvasive monitoring with a laser-Doppler flowmetry and spectrophotometry unit (O2C) and identify whether perioperative blood flow, velocity, hemoglobin level (Hb), and oxygen saturation (SO2) measured could be used as indicators of free flap success. Measurements of blood flow, velocity, Hb, and SO2 were performed in 196 microvascular flaps, which had been transferred into the oral cavity to reconstruct ablative defects after surgery for oral cancer. The values were calculated superficially on the skin surface and at a depth of 8 mm. The results showed that perioperative absolute values measured were not associated with an increased rate of microvascular revisions or free flap failure. Independent predictors of microvascular revisions at the first postoperative day were the development of a falling trend in superficial and deep blood flow, and velocity in comparison with baseline values of variables measured. On day 2, all superficial and deep values of Hb, flow, and velocity were independent prognostic factors (P < 0.01), demonstrated as a downward trend were associated with a need for revision. The superficial and deep values of SO2 (P = 0.59 and 0.43, respectively) were not associated with ultimate free flap failure. This is the first clinical study to demonstrate that during early free flap integration to the recipient site different parameters of perfusion and oxygenation play an important role at different points of time. Within the first two postoperative days, changes in these parameters can help influence the decision to revise microvascular anastomoses. © 2013 Wiley Periodicals, Inc. Microsurgery 34:345–351, 2014.