Objective:To describe the occurrence of immediate transfusion reactions received by the Risk Management Department of Hospital São Paulo. Method: Cross-sectional and retrospective study which analyzed the notification sheets of transfusion reactions that occurred between May 2002 and December 2016 and were included in the Hemovigilance National System. Results: One thousand five hundred and forty-eight transfusion reaction notification sheets were analyzed, all of which concerned immediate reactions associated with packed red blood cells (72.5%). The most frequently reported reaction was febrile non-hemolytic transfusion reaction, and among severe and moderate cases, allergic reaction was the most common. The most frequently reported signs and symptoms were hyperthermia, sudoresis, chills, and skin lesions. No differences were observed regarding gender and age, and 90.7% of reactions occurred in patients with Rh+ factor. Conclusion: This study allowed for a better assessment and understanding of transfusion reactions, which will help to improve the quality of blood circulation and provide greater safety of patients undergoing transfusion therapy.