Transfusion of the wrong blood is a rare but measurable event that may result in serious complications and whose main cause is human error. Any preventive strategy should be based on a careful assessment of the incidence of these events and of their causes, and requires a standardized confidential reporting system, to avoid underreporting, covering also near misses. Creating or revising written procedures and monitoring their implementation are indispensable to improve blood safety, but human error can occur in spite of these measures. Technologic instruments are now available to fill the gap between written and implemented procedures, forcing the operator to carry out the critical steps in the process according to the adopted guidelines.