BACKGROUND The sirolimus-eluting stent (SES) has dramatically reduced the rate of restenosis in comparison to that with the bare-metal stent (BMS). In previous studies, the minimal luminal diameter (MLD) of lesions treated with a BMS was shown to improve from 6 months to 1 year. METHODS To evaluate 6-month and 1-year outcomes, angiographic follow-up data were analyzed for 285 patients (451 lesions) who underwent successful SES implantation compared to follow-up data for 2,561 patients (3,367 lesions) who underwent BMS implantation. RESULTS Angiographic follow-up was performed at 6 months for 396 SES-treated lesions and 2,628 BMS-treated lesions and at 1 year for 322 SES-treated lesions and 1,540 BMS-treated lesions. The 6-month angiographic restenosis rate was significantly lower for SES-treated lesions than for BMS-treated lesions (4.8% vs. 23.4%, p<0.01). From immediately after stent implantation to 6 months, quantitative coronary angiography revealed a significantly larger decrease in MLD of BMS-treated lesions than in MLD of SES-treated lesions (p<0.01). In BMS-treated lesions in which repeat revascularization was not performed at 6 months, MLD increased significantly from 2.08+/-0.63 mm at 6 months to 2.11+/-0.61 mm at 1 year (p<0.01). In SES-treated lesions, however, MLD decreased significantly from 2.55+/-0.56 mm at 6 months to 2.44+/-0.61 mm at 1 year (p<0.05). CONCLUSIONS From 6 months to 1 year, stenosis of BMS-treated lesions regressed, but stenosis of SES-treated lesions progressed.