Background and Objectives: Even though Blood Transfusion Service is considered as life-saving intervention, it is associated with the occurrence of uneventful reactions from the transfusion of blood and blood units. Bhutan Blood Bank is fragmented with different levels of services provided which leads to varied levels of adverse blood transfusion reaction reported. Study on the hemovigilance system at tertiary care hospital is conducted so as to study the frequency and types of reactions over a period of three years from 1st January 2019 to 31st December 2021. Methods: All ATRs occurring within a period of 3 years were studied according to the Blood Bank standard operating procedure. Adverse transfusion events related to blood and blood units were analyzed and classified on the basis of their clinical features and laboratory tests. Descriptive statistics were used to represent the adverse transfusion reactions. Results: During this period, a total of 19,961 blood and blood components were issued and 120 adverse transfusion events were reported. Most reaction reported were febrile non-hemolytic transfusion reaction, FNHTR (59.2%) followed by allergic reaction (22.5%) occurring predominantly in females (93%). Packed red cells were the common component causing adverse events (83 %) with most observable in Group A (42.5%) blood units. Conclusion: Febrile and allergic reactions are the most common type of reaction reported. Although such reaction type is least harmful but fatal reaction can occur and preventive measures must be taken to avoid such reactions. This preliminary study indicates the importance of having continuous monitoring and quality assessment scheme in addressing the issues of adverse transfusion reaction. Furthermore, establishing a hospital transfusion committee is vital for delivery of safe and efficient blood transfusion services.