Background: Blood and apheresis donations are widely considered safe, with a low incidence of adverse reactions and injuries. However, data reported in the medical literature on the prevalence of adverse events in donors and studies on the predictive risk factors for donor reactions are limited and contradictory. Material and Methods: From January 1998 to June 2001, we recorded at our transfusion center all adverse events occurring during 116,952 consecutive blood and apheresis donations (homologous and autologous whole blood donation, plasmapheresis and plateletpheresis). Results: 1,960 adverse events were reported (1.7% of all donations). With a frequency of 1.2%, vasovagal reactions, mostly of mild intensity, were the most commonly observed adverse event. The frequency of vasovagal reactions was significantly lower in autologous blood and apheresis donations than in homologous blood donations. Hematoma at the venipuncture site was the second most frequent adverse effect with a rate of 0.4%. A mild to moderate citraterelated toxicity was observed in 0.3% of apheresis donations. With an overall rate of 0.02%, severe adverse reactions (vasovagal, citrate-related and cardiopulmonary events) were very rare. No life-threatening adverse effect was reported, and no severe adverse event required hospitalization. Finally, we found that those donors who experienced adverse reactions were primarily first-time donors, were younger, and had a lower weight and predonation blood pressure than donors without reactions. Conclusions: Blood and apheresis donations are safe procedures with a low incidence of adverse reactions. Young age, first-time donation status, low weight and predonation blood pressure are predictive factors of donor reactions.