Background: There are few data that demonstrate a significant effect of aspirin therapy for diabetic patients. To clarify the effect of the primary prevention of aspirin therapy in diabetic patients, the relationship between blood pressure (BP) and the incidence of atherosclerotic events was investigated in participants in the Japanese primary prevention of atherosclerosis with aspirin for diabetes (JPAD) trial. Methods and Results: We divided the JPAD participants according to their systolic (SBP) and diastolic (DBP) BPs at enrollment (SBP Y140mmHg and/or DBP Y90mmHg: unattained group, SBP <140mmHg and DBP <90mmHg: attained group). The incidence of the primary atherosclerotic events, especially cerebrovascular events, was higher in the unattained group than in the attained group. The incidence of cerebrovascular events was higher in the unattained group than in the attained group in patients without aspirin therapy; however, the incidence of cerebrovascular events in the unattained group was as low as the incidence in the attained group in patients undergoing aspirin therapy. Cox proportional hazards analysis revealed that BP level was an independent predictor for cerebrovascular events in diabetic patients. Conclusions: Aspirin therapy may reduce cerebrovascular events in diabetic patients with higher BP. Aspirin therapy could be an additional strategy as primary prevention for diabetic patients with higher BP. (Circ J 2012; 76: 1526-1532)