A growing body of evidence suggests that episodes of fainting can deter volunteer blood donors from returning to donate in the future. In contrast, relatively little is known about the effect of significantly more common mild reactions (e.g., faintness, dizziness, lightheadedness) on donor retention. In the present study, 1052 volunteer blood donors completed a standardized measure of subjective physiological reactions immediately after blood donation (Blood Donation Reactions Inventory), and individual scores were used to predict repeat donation behavior during a one-year follow-up. Results of a logistic regression analysis indicated that higher scores on the Blood Donation Reactions Inventory were associated with a significantly lower likelihood of repeat donation, and that novice donors who scored highest on the scale were less than half as likely to have returned to donate in the following year. These findings suggest that the Blood Donation Reactions Inventory is an effective method of assessing reactions that predict donor non-return, and therefore may be a useful addition to future studies aimed at enhancing donor satisfaction and retention.