In a randomized double-blind trial, the Study Group compared the efficacy of E5510, a novel antiplatelet agent, and aspirin in preventing the recurrence of transient ischemic attacks (TIA). In total, 227 patients who suffered from TIA in the twelve weeks prior to the study were enrolled. They were randomly allocated to three treatment groups, ie, 71 patients in the E5510 4 mg group, 77 patients in the E5510 2 mg group, and 79 patients in the aspirin 324 mg group, and were treated for twelve to twenty-four weeks. The incidence of recurrent TIA or stroke was 21.5% in the aspirin group and was significantly lower in the E5510 groups, being 8.5% in the 4 mg group (P < 0.05) and 11.7% in the 2 mg group (P < 0.05). Adverse events were observed in 5 cases in the 4 mg group, in 8 cases in the 2 mg group, and in 10 cases in the aspirin group, but none of them were serious. Since safety was judged to be comparable among the three groups, E5510 appears to be an antiplatelet agent for the treatment of TIA with a clinical benefit over aspirin.