Background: Despite advances in the monitoring of free flaps, there is still a demand for new technology to detect ischemic complications at an early stage. The aim of the present study was to evaluate the reliability of the O2C‐device in terms of detecting flap failure in commonly used perforator flaps for breast reconstruction.Methods: A total of 34 patients undergoing breast reconstruction were involved in this study. The perfusion dynamics of 23 deep inferior epigastric perforator flaps and 11 superior gluteal arterial perforator flaps were assessed using the O2C‐device, which combines a laser light, to determine blood flow (flow), velocity, and white light to determine hemoglobin oxygenation (SO₂) and relative amount of hemoglobin (rHB). Measurements were carried out intra‐operatively after clamping and declamping the perforator vessels. In the post‐operative period measurements were carried out every hour for the first 48 hours and from 3rd to 7th for every 2 hours. These dates were compared to findings of clinical assessment.Results: Several intra‐operative measurements, during the clamping and declamping the different perforator vessels, revealed a high correlation for all parameters: Flow (r = 0.89, P < 0. 05), Velo (r = 0.92, P < 0. 05), SO₂ (r =0.84, P <0. 05), and rHB (r =0.83 P < 0.05). Vessel occlusion was detected in five cases, of which three were due to arterial thrombosis and two further cases were due to venous occlusion. Of the five cases, one flap loss caused by venous occlusion was noted.Conclusion: The O2C‐device seems to be a reliable, objective, and non‐invasive device for the monitoring of free flaps. Thus, it may improve flap survival rates by detecting vascular compromise at an early stage. © 2013 Wiley Periodicals, Inc. Microsurgery 33:350–357, 2013.