The present study examined the relative importance of the aversiveness of the donation procedure, donor motives and donor personality characteristics in the blood donors' decision to donate. One hundred and eighty-six blood donors and 106 nondonors took part in this retrospective study. Participants were asked to complete a number of personality measures, and two questionnaires assessing their motives for donating and the aversiveness of their most recent donation experience. Results indicated that both the aversiveness of the donation procedure and the donor's motivation exert considerable influence upon the donors' decision to return and donate again. Additionally, the donors' experience of physical discomfort and fearfulness about the donation procedure made the major contributions to the donation's aversiveness. The results also revealed that significant differences exist among nondonor, ex-donor, irregular and regular donor groups on several personality characteristics, on their motives for donating, and on the components comprising the aversiveness of the donation procedure. A blood donor decision model is presented incorporating the influence of motivational, situational and dispositional factors in the individual's development into a regular donor.