Background: The optimal time delay between last clopidogrel dose and surgery is controversial. The aim of the present study was to analyze the impact of preoperative clopidogrel on the need for blood transfusions with reference to the proper timing of discontinuation. Methods and Results: Between January 2005 and December 2010, 1,947 consecutive patients undergoing coronary surgery were enrolled. Of these, 255 patients receiving preoperative clopidogrel were matched to a control group by propensity score analysis. Clopidogrel discontinuation interval before surgery was examined in 1-day increments from 0 to 5 days and >5 days. Patients who discontinued clopidogrel within 5 days of surgery accounted for 91% (211/255). Clopidogrel stop within 5 days before surgery was independently associated with transfusion requirement (P=0.001). Preoperative clopidogrel was not associated with an increased risk of hemorrhagic complications (P=0.696). No differences were observed between patients taking clopidogrel and those not taking clopidogrel with regard to hospital resource utilization and mortality. Patients receiving clopidogrel in association with aspirin did not have an additive risk for transfusion or hemorrhagic complications compared with those on clopidogrel alone (odds ratio [OR], 1.25; 95% confidence interval [CI]: 0.77-2.03; OR, 1.02; 95%CI: 0.38-2.79, respectively). Conclusions: Clopidogrel administration in the 5 days preceding coronary surgery was an independent predictor for increased transfusion requirements, supporting the discontinuation of clopidogrel >5 days before surgery. (Circ J 2011; 75: 2805-2812)