Transfusion of blood components is considered safer, but it took years to reach this level. One of the most effective ways to make blood transfusion a safer practice is hemovigilance, which provides important data, including the history of feared transfusion reactions. In recent years in Brazil, there has been an improvement in the reporting of transfusion reactions, however due to the great diversity of hematology services, there are still transfusion reactions. The aims of this study were described the main types of transfusion reactions, as well as to evaluate the underreporting importance of transfusion occurrences of hemotherapy services in Brazil.