ABSTRACT Background: Blood transfusion is a life-saving procedure, but may cause adverse transfusion reactions (TRs). The reporting of TRs is often missed due to various reasons. The aim of this study was to determine the incidence of unreported acute TRs through active surveillance and to compare it with the incidence of passively reported TRs. Methods: This prospective observational study was done over a period of four months at a tertiary care hospital. A total of 500 consecutive transfusion episodes (TEs) in patients who had received blood component transfusions in the intensive care units were included in the study. Comprehensive data were collected from the blood bank records, patient records and through interviews with the attending clinical staff. The TEs were defined as all blood components issued to a single patient in 24 h. Results: The overall incidence of TRs was 1.8 % (9 cases), with 0.4 % (2 cases) being reported passively, while 1.4 % (7 cases) were identified during active surveillance. The transfusion-associated cardiac overload (TACO) had the highest incidence of 1.2 % (6 cases) in active surveillance. A single case of acute hemolytic transfusion reaction was also observed during active surveillance. The passively reported TRs were one allergic reaction and one febrile non-hemolytic transfusion reaction. Conclusion: Active surveillance of TRs provided an insight into the true incidence of TRs, which is higher when compared with the passively reported TRs. The TACO was found to have the highest incidence and not a single case was reported. There is a need to improve awareness regarding TR reporting.