Objective: Platelet dysfunction has been shown to play a role in postoperative bleeding; however, it is not clear whether immature platelets (IP) can induce appropriate homeostasis to prevent excessive bleeding in patients undergoing CABG. This study investigated IP count (IPC), IP fraction (IPF) and mean platelet volume (MPV) throughout the hospitalization of patients undergoing CABG to elucidate their impact on postoperative bleeding and need for transfusion. Methods: Fifty consecutive patients undergoing elective CABG were included in this prospective study. All CABGs were performed by the same surgical team in a standardized fashion utilizing on-pump technique. IP and IPF were measured preoperatively, after the completion of surgery and at postoperative 1st,3rd, and 5th days. Whether need for transfusion was associated with IP, IPF, MPV and platelet count was the primary outcome measure of this study. Results: A significant increase in IPC and IPF was observed at the postoperative first day compared to baseline values. Preoperative IP and IPF were negatively correlated with intraoperative blood transfusion (p=0.017, and p=0.049, respectively). Duration of the operation, and preoperative hemoglobin and hematocrit levels were significantly correlated with the length of hospital stay. However, neither IP nor IPF were associated with the total amount of blood components used throughout the hospitalization, and they were also unassociated with the length of hospital stay. Conclusion: Although IPC and IPF are weakly correlated with postoperative drainage and blood transfusion frequency, they appear to have very little use –if any– in the prediction of postoperative bleeding in patients undergoing CABG