Medicinal products containing monoclonal antibodies are highly specific and they have been used mainly for the diagnosis and therapy of autoimmune diseases and cancer for the past ten years. However, the use of monoclonal antibodies can cause hypersensitivity reactions. Typically, these reaction manifest on the skin and generally have favorable outcomes. Nevertheless, systematic monitoring of hypersensitivity reactions is necessary in order to optimize the benefit-harm ratio of their use. The Croatian Agency for Medicines and Medical Products (HALMED) maintains a comprehensive database encompassing all adverse effects, including hypersensitivity reactions. This thesis analyzes cases of reported hypersensitivity reactions to monoclonal antibody-based medications reported to HALMED. Adverse reaction reports were analyzed by year of receipt, reporter, seriousness, seriousness criteria, age and gender of a patient, preferred term, as well as the active substance. By May 15, 2023, HALMED had received 3,859 reports of adverse reactions to monoclonal antibodies, with 62.3% classified as serious. Of these reports, 796 (equivalent to 20.6% of all reports) corresponded to hypersensitivity reactions to monoclonal antibodies. Medical professionals constituted the primary reporters of hypersensitivity reactions, accounting for 86.3% of the reports. Hypersensitivity reactions were more frequently reported among female patients (49.1%) and adults aged 45 to 64 (29.8%). A majority of the documented hypersensitivity cases were categorized as non-serious (54.1%). Commonly reported symptoms included rash, erythema, and pruritus. The active substances most frequently associated with hypersensitivity reactions were infliximab, pembrolizumab, and adalimumab. According to the results of this thesis, hypersensitivity reactions are frequently reported side effects, while compared to other reported side effects, a smaller proportion of reported side effects are assessed as serious. These results highlight the importance of comprehensive monitoring and evaluation of hypersensitivity reactions to medicinal products containing monoclonal antibodies to ensure their safe and effective utillization in clinical practice.