Vascular thrombosis implicates in the pathogenesis of pulmonary arterial hypertension (PAH). Anticoagulation therapy (warfarin) has been recommended by many experts in the treatment of PAH. However, the long-term effectiveness of anticoagulation therapy remains controversial. Because of the various drugs, such as epoprostenol, bosentan, and sildenafil, for the treatment of PAH recently, warfarin alone is not a realistic therapy for PAH. Accordingly we reviewed the previous manuscript regarding anticoagulation therapy for PAH, and looked at the current role of anticoagulation therapy in Japan.