Thrombocytopenia is a common finding in critically ill patients. Heparin-induced thrombocytopenia is an infrequent cause of a low platelet count. Intensivists should use the diagnostic classification system developed by the International Society on Thrombosis and Haemostasis to diagnose heparin-induced thrombocytopenia. The clinical relevance of the presence of anti-heparin/platelet factor 4 complex autoantibodies in the absence of clinical heparin-induced thrombocytopenia remains unknown.