ABSTRACT Heparin-induced thrombocytopenia and associated thrombosis (HIT/HITT) is a potentially lifethreatening complication of therapy with unfractionated and low-molecular-weight heparins. The aim of this study was to systematize reported clinical cases of HIT/HITT and to analyze current approaches to its diagnosis. A review of observational series and individual clinical cases published over the last 10 years was performed. The main clinical manifestations of HIT/HITT included venous and arterial thrombosis, accompanied by the development of severe complications in some patients. Diagnosis was based on clinical assessment using the 4T score and laboratory testing, including PF4-ELISA and functional platelet activation assays. Data analysis demonstrated a higher incidence of HIT/HITT associated with the use of unfractionated heparin compared with low-molecular-weight heparins. The findings highlight the importance of early identification of patients at high risk and timely modification of anticoagulant therapy. Keywords: Heparin-induced thrombocytopenia, HIT, HITT, platelet factor 4, thrombosis, alternative anticoagulation, direct thrombin inhibitor, fondaparinux, diagnosis, management.