Dabigatran is a direct thrombin inhibitor, does not require blood coagulation monitoring and limitation of vitamin K intake as well as very few drug interactions, and thus expected to be an oral anticoagulant alternative to warfarin. Randomized Evaluation of Long Term Anticoagulant Therapy (RE-LY) was conducted to determine non-inferiority of dabigatran against warfarin as an international multicenter-cooperative randomized trial in patients with non-valvular atrial fibrillation (NVAF). The results showed not only non-inferiority of dabigatran but also superiority of high-dose dabigatran in efficacy and of low-dose dabigatran in safety. In a sub-analysis of RE-LY in NVAF patients with history of stroke or TIA, who are at high risk of intracranial hemorrhage with anticoagulants, hemorrhagic stroke was much less frequent in patients on either dose of dabigatran than in those on warfarin. In a sub-analysis of RE-LY in Japanese patients with NVAF, the results showed a consistency of the efficacy and safety profiles of dabigatran with the results of the global RE-LY trial. Use of dabigatran should be contraindicated in NVAF patients with renal insufficiency because some cases with fatal bleeding have been reported in a post marketing survey.