Rapid communication regarding the proper use and safety of dabigatran has indicated the possibility of potentially fatal severe hemorrhagic side effects. We analyzed the safety and risks of hemorrhagic side effects associated with longterm dabigatran administration．We investigated 112 inpatients and outpatients who had received dabigatran between July 2011 and March 2013 for newly acquired non-valvular atrial fibrillation, and obtained information on patient background, dose, use of combined drugs, and side effects. Patients were allocated to groups receiving 220 mg or 300 mg dabigatran, and to groups who developed hemorrhagic or non-hemorrhagic side effects. Patients were significantly older in the 220 mg dabigatran group than in the 300 mg group (P < 0.0001), and Ccr before administration was significantly lower in the former than in the latter (P = 0.0002). The incidence of side effects was 26.8％, gastrointestinal symptoms being the most common at 14.3％. Hemorrhagic side effects occurred in 11.6％ of patients, and all involved minor bleeding. The number of patients receiving antiplatelet drugs was also significantly higher in the hemorrhagic side effects group than in the non-hemorrhagic side effects group (P = 0.04). We conclude that the dose of dabigatran should be selected based on age and renal function due to the prevention of severe side effects for long periods. Although all hemorrhagic side effects involved minor bleeding, it is considered advisable to be aware of antiplatelet drugs used in combination.