The haemovigilance system has indirectly introduced three types of information: a more precise tally of accidents and risks (even if the total number of events remains difficult to assess); an evolution of the mode of collecting relevant information (even if, after 3 years, it has become important to define new objectives and collection procedures); the identification of the main causes of errors leading to immunological accidents allowing the elaboration of schemes pointing out the possible failures and critical points of the various processes, such as blood bag distribution, ABO control at bedside, the prescription of examinations prior to transfusion. The analysis of haemovigilance data has induced a number of important consequences, particularly clinical practitioners' awareness of blood transfusion risks; elaboration of reliable and documented tools for the training of professionals and the information of patients; implementation of corrective and preventive measures, particularly to reduce accidents due to ABO incompatibility. These haemovigilance data will provide more fruitful results when cross-analysed with data from the reactovigilance system which is being set up. Until then, they will largely be used to elaborate blood transfusion quality assurance standards.