Clopidogrel is an oral thienopyridine that has been shown to reduce the risk of vascular death in patients with acute coronary syndrome, ischemic stroke, and peripheral vascular disease. The drug is associated with rare adverse effects such as thrombotic thrombocytopenia purpura, acute hepatotoxicity, and neutropenia. Only six cases have been reported that link acute arthritis with the use of clopidogrel. We describe a 64-year-old Caucasian man with sudden onset of severe arthritis, erythema, and swelling after starting clopidogrel therapy; he had no history of arthralgias while taking prasugrel during the previous 8 months. The patient was hospitalized for 3 days, and after cessation of clopidogrel therapy and conservative management, he improved dramatically, showing resolution of his joint erythema and swelling. The patient started prasugrel therapy at discharge, and no arthritic development was noted 8 weeks later. Although clopidogrel is commonly well tolerated, this case report demonstrates that clinicians should be aware that acute arthritis may be a possible adverse effect of clopidogrel. Additionally, polyarthralgias may not be a class effect of thienopyridines; patients who experience acute arthralgias during clopidogrel therapy may not experience similar adverse effects with prasugrel.