Clopidogrel has replaced ticlopidine (in the United States but not worldwide). Clopidogrel can either be used independently or in combination with other antiplatelet agents. Clopidogrel has a lower frequency of associated thrombotic thrombocytopenic purpura than ticlopidine, a lower rate of neutropenia, and better gastrointestinal tolerance. We describe a case of thrombotic thrombocytopenic purpura associated with the use of clopidogrel after percutaneous transluminal angioplasty and stent placement. Discontinuation of the drug and transfusion of 17 units of cryodepleted plasma resulted in resolution of the hematological abnormalities. Clinicians should be alert to this adverse effect of clopidogrel and monitor platelet counts in patients receiving it.