Unlike essential thrombocytosis, which is associated with thrombotic and hemorrhagic complications, reactive thrombocytosis (RT) is usually considered a benign process without thrombotic complications. We describe a case of acute myocardial infarction in a young heavy smoker with RT following splenectomy. Coronary angiography showed a linear filling defect at mid-part of left anterior descending artery. We performed balloon angioplasty and stenting for this lesion. Aspirin and clopidogrel were administered. His in-hospital course was uneventful and platelet count returned to the normal range at four month follow-up. We concluded that RT may not be an entirely benign process, especially in patients with a history of smoking. Regular monitoring of platelet count, and possibly antithrombotic agents like aspirin prescription for high risk patients with moderate thrombocytosis, may be useful.