This article about treatment and prevention of stroke is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading, see the "Grades of Recommendations" chapter by Guyatt et al, CHEST 2008; 133:123S-131S). Among the key recommendations in this chapter are the following: For patients with acute ischemic stroke, we recommend administration of IV tissue plasminogen activator (tPA) if treatment is initiated within 3 h of clearly defined symptom onset (Grade 1A). For patients with acute ischemic stroke of > 3 h but < 4.5 h, we suggest clinicians do not use IV tPA (Grade 2A). For patients with acute stroke onset of > 4.5 h, we recommend against the use of IV tPA (Grade 1A). For patients with acute ischemic stroke who are not receiving thrombolysis, we recommend early aspirin therapy (Grade 1A). For acute ischemic stroke patients with restricted mobility, we recommend prophylactic low-dose subcutaneous heparin or low-molecular-weight heparins (Grade 1A). For long-term stroke prevention in patients with noncardioembolic stroke or transient ischemic attack (TIA) [ie, atherothrombotic, lacunar, or cryptogenic], we recommend treatment with an antiplatelet agent (Grade 1A), including aspirin (recommended dose, 50-100 mg/d), the combination of aspirin and extended-release dipyridamole (25 mg/200 mg bid), or clopidogrel (75 mg qd). In these patients, we recommend use of the combination of aspirin and extended-release dipyridamole (25/200 mg bid) over aspirin (Grade 1A) and suggest clopidogrel over aspirin (Grade 2B), and recommend avoiding long-term use of the combination of aspirin and clopidogrel (Grade 1B). For patients who are allergic to aspirin, we recommend clopidogrel (Grade 1A). In patients with atrial fibrillation and a recent stroke or TIA, we recommend long-term oral anticoagulation (target international normalized ratio, 2.5; range, 2.0 to 3.0) [Grade 1A]. In patients with venous sinus thrombosis, we recommend unfractionated heparin (Grade 1B) or low-molecular-weight heparin (Grade 1B) over no anticoagulant therapy during the acute phase.