Heparin-induced thrombocytopenia is a prothrombotic adverse effect induced by platelet-activating antibodies against complexes of platelet factor 4 and heparin. Diagnosis rests on a clinical assessment of disease probability and laboratory testing. In this review, I describe some approaches to the evaluation of patients with suspected heparin-induced thrombocytopenia. In conclusion I draw attention to some of the reserves in the diagnostic approaches to this potentially fatal disorder in the Czech Republic.