BACKGROUND: Donor selection is still being emphasized, even in the era of sensitive laboratory screening. Therefore, a number of volunteers are deferred from blood donation. This study evaluated the deferral rate in Iran, as well as the frequency of each reason in order to monitor the impact of donor selection process on donor loss.METHODS: This study was carried out on data of all volunteers who were deferred from blood donation in Isfahan Blood Transfusion Services between the years 2007 – 2008. The deferral reasons were then classified into “donor safety” and “recipient safety”. The total deferral rates within sociodemographic variables and donor status were compared. Then, the rates of various specific deferral reasons were calculated.RESULTS: Out of 197,757 blood donor volunteers, 50,727 (25.6%) were deferred from donation; 88.6% were temporarily deferred whereas 11.4 % were permanently deferred. The deferral rate for females and males was 54.6% and 24.3%, respectively. Forty-three percent of the first-time donors, 9% of the lapsed donors, and 11.9% of the regular donors were deferred. Sixty-one percent of all deferrals were due to donors' safety while 31% were deferred due to recipients’ safety.CONCLUSION: Blood donors' deferral rate in Iran was significantly higher than other countries. This may be due to special attention to donor selection procedures. However, revision of the national criteria of donor selection and rigorous adherence to these criteria should be considered. Also, it is emphasized to improve the blood donor retention strategies to boost the regular blood donors’ pool.