Background : In-stent restenosis following coronary artery stenting, mainly attributable to neointimal hyperplasia and thrombus formation, remains a major limitation of the procedure. Recently, cilostazol was reported to have antiproliferative properties and reduce restenosis after coronary angioplasty and stenting. Methods : This study was designed to investigate the efficacy of triple combination of aspirin, ticlopidine, and cilostazol for the prevention of in-stent restenosis in comparison with aspirin plus ticlopidine. Fifty-three consecutive patients (36 men, age 63 years), scheduled for elective coronary stenting, were randomly assigned to receive a drug regimen with aspirin and ticlopidine plus 100 mg bid cilostazol ( A+T+C group, n=28 ) or aspirin plus ticlopidine ( A+T group, n=25 ). Initial and follow-up quantitative coronary angiography(QCA) and volumetric intravascular ultrasound(IVUS) were performed after PCI and at 6 months. Only one type of stent ( Express stent, Boston Scientific) was used for this study. The primary endpoint was MLD at 6 months and intimal hyperplasia index (intimal hyperplasia volume / stent length ). Results : Fifty-eight coronary lesions in fifty-three patients were analyzed by QCA ( 31 in A+T+C group, 27 in A+T group ), and 35 lesions were analyzed by volumetric IVUS ( 20 in A+T+C group, 15 in A+T group ). There were no significant differences in mean reference diameter, initial MLD, stent diameter, stent length and post-stent MLD at initial angiography between the two groups. At 6 months follow-up, in-stent MLD(mm) was 2.38 in A+T+C group versus 1.90 in A+T group (p=0.033). The volumetric IVUS at 6 months demonstrated that intimal hyperplasia index (mm쨀/mm) was 1.02 in A+T+C group and 1.97 in A+T group(p=0.003). The binary restenosis rate was not statistically different between the two groups but slightly lower in the A+T+C group than the A+T group (13% vs. 26%, p=0.177). Conclusions : This study showed that the triple antiplatelet therapy including cilostazol reduced the rate of in-stent restenosis after coronary stent implantation.