This study analyses the variables associated with the decisions made by families of potential organ donors to give or deny consent for the extraction of organs. Different indicators were recorded in 68 cases of family interview for petition of consent carried out in 13 Spanish hospitals. Those variables showing the strongest relation with family decision (donation/refusal of consent) are knowledge shown by the family about the deceased's wishes with regard to donation (p<0.001), family relationship climate (p<0.01), expression of family's satisfaction level with medical attention received (p<0.01) and number of relatives present at the consent request interview (p<0.01). Logistic regression on family decision with considered variables correctly predicted relatives' final choice in 98.4% of cases. In turn, multivariate exploratory analysis highlights a potential association between the expression of the deceased's wishes and several concurrent variables in the process (satisfaction with personal treatment and medical attention received, emotional reactions in the interviews of notification of death and consent request). It also shows that patterns of reaction and family participation in this process may vary according to the sex of the deceased relative. Results suggest that both educational efforts devoted to promoting a positive attitude toward donation in the general population and the training of health professionals involved in the generation of organs may be key factors in reducing organ shortage.