Background: The effect of cilostazol on long term clinical outcomes in diabetic patients who underwent drug-eluting stent (DES) implantation was not evaluated. Methods and Results: A total of 100 patients were randomized. The patients who underwent successful stenting were randomized to aspirin (100~200 mg qd) and cilostazol (100 mg bid) (group I, n= 46, mean 63.4짹9.4 years old, 24 males) vs. aspirin and clopidogrel (75 mg qd) (group II, n=54, mean 63.3짹10.0 years old, 24 males) after one month of aspirin, cilostazol, and clopidogrel combination treatment and treated for one-year. Baseline patient characteristics were not different between the two groups. The types of DES implanted were not different between the groups (9 Cypher and 37 Taxus in group I vs. 10 Cypher and 44 Taxus in group II, p=0.894). There were no differences in angiographic and procedural characteristics between the groups. Major adverse cardiac events (MACE) including acute and subacute stent thrombosis within one month were not developed in both groups. According to the follow-up coronary angiogram, in-stent restenosis (stent plus 5-mm borders) was (n=7, 15.2 %) in group I and (n=11, 20.4 %) in group II, (p=0.504). The minimal luminal diameter at follow-up coronary angiogram in group I was 2.17짹0.15 mm compared with 2.10짹0.12 mm (p=0.692) in group II. The incidence of target lesion revascularization in group I was 4 (8.7 %) and that in group II was 8 (14.8 %). Incidence of target vessel revascularization in group I was 1 (2.2 %) and that in group II was (5.6 %) (p=0.203). The incidence of De novo lesion at any vessel was in group I was n=7 (15.2 %) and that in group II (n=9, 16.7%) (p=0.844). At 1-year clinical follow-up, the incidence of cardiac death and Q-wave myocardial infarction were not observed both group. The serious side effects were not observed in both groups, too. Conclusions: Our results demonstrated that the effects of combination therapy with aspirin and cilostazol for the prevention of acute and subacute stent thrombosis, in-stent restenosis and one year cardiac death and Q-wave myocardial infarction were comparable to those of aspirin and clopidogrel.