The aim of the study was to estimate the type, incidence and causes of donor adverse reactions during and after blood donation in a Greek Blood Bank, where medical staff is responsible for donor selection. 12 173 blood donors were studied for adverse reactions. One-hundred and seven (0.87%) donors had a vasovagal reaction during or after blood donation. Donors who gave blood occasionally had a significant greater incidence of reactions compared with volunteer donors (1.15 versus 0.53%) (P < 0.001). There was no significant difference between men and women (0.85 versus 0.95%). First-time donors (1.7 versus 0.68%) and those under 30 years (1.15 versus 0.71%] had a significant greater possibility to have a reaction (P < 0.001). Twenty-two of 107 (20.5%) donors had a syncopal reaction. There was not a causative correlation of haematocrit, haemoglobin, systolic and diastolic blood pressure, pulse rate and weight in women (except weight in men) in developing a reaction. The stressing experience of phlebotomy was the reason for the higher frequency of a reaction. The incidence of reactions in our donors is lower than in other studies, and the possible reason for this is that only physicians are responsible for the selection of donors and trained personnel are careful of them during the donation process.