The case is described of a 71-year-old woman presenting with acute erosive lichen planus. The lesions appeared one week after starting treatment with clopidogrel (Plavix), a new antiplatelet drug, for the prevention of cerebral thrombosis. The patient presented erosive lesions on both jugal mucosal surfaces and the lateral sides of the tongue, associated with intense pain. The clinical diagnosis of erosive lichen planus induced by clopidogrel was confirmed by histological biopsy evaluation. Clopidogrel was replaced by aspirin, which was the antiplatelet drug previously used by the patient, and 0.1% triamcinolone acetonide in orabase was prescribed in combination with systemic corticoids. The erosive lesions and pain disappeared as a result, though asymptomatic reticular lesions typical of lichen planus persisted.