A meta-analysis by the Antithrombotic Trialists' Collaboration showed significant reduction of vascular events including stroke. MI, and vascular death by antiplatelet therapy in high risk patients with obstructive vascular disease. Low dose aspirin of 75 to 150 mg was most effective and its very low dose below 75 mg was not proven effective. Cilostazol significantly reduced the risk of recurrence in Japanese patients with ischemic stroke, mostly lacunar stroke. Large randomized controlled trials (RCTs) such as MATCH, ACTIVE, and CHARISMA are ongoing to see an effect of aspirin plus clopidogrel. Among patients with non-valvular atrial fibrillation (NVAF), warfarin is recommended in patients at age over 75 years, and those with history of stroke or TIA, hypertension, congestive heart failure, diabetes or coronary heart disease, while aspirin can be alternative in patients without any of these risk factors of stroke. Target INR of 2.0 to 3.0 is recommended in these NVAF patients, although lower INR of 1.6 to 2.5 is recommended to avoid hemorrhagic stroke in elderly patients with NVAF. SPORTIF was conducted to compare ximelagatran, an oral thrombin inhibitor, with warfarin in NVAF patients with risk factors, and the result showed a comparable efficacy and safety of ximelagatran. WARSS did not show any efficacy of warfarin over aspirin in any subtypes of ischemic stroke patients without NVAF, acute MI, left ventricular thrombi, or prosthetic heart valve. PICSS, a substudy of WARSS, also did not show any efficacy of warfarin over aspirin in stroke patients with patent foramen ovale (PFO), although warfarin might be recommended in PFO patients with deep vein thrombosis.