Introduction: Perioperative transfusions are associated with complications of free flaps. The purpose of the present study was to find out whether there is a significant relationship between the risk of developing complications in vascular anastomoses and the history of transfusions. Methods: We studied 372 patients retrospectively with microsurgical reconstruction between 2009 and 2017 with regards to the number of red blood cell concentrates transfused. Complications were analyzed relative to flap loss and complications in microvascular anastomoses. Results: 130 patients (34.9%) received blood transfusions. Some 55% of them were transfused between the day of the intervention and the first postoperative day. Ninety-six patients were reoperated on (25.7%). Of those, thirty-six patients (37.5%) corresponded to anastomosis failure. The percentage of patients transfused among those who required reoperation was 55.2%. The percentage of patients transfused among those who were reoperated on within the first 72 h due to an alteration in the anastomosis was 60.6%, while it was 25.6% (Chi square P = 0.0001) for the rest of the patients. Conclusions: Although there is a strong association between transfusion and vascular anastomosis failure, it is not possible to establish the causation between the two.