Background: Sirolimus-eluting stent (Cypher���, Cordis; SES) significantly reduced the rate of restenosis after stent implantation. And cobalt based thinner-strut stents (CTSS) are reported to have lower rate of restenosis than conventional bare metal stent. The present study was performed to compare the angiographic and clinical results of SES and CTSS (Driver���, Medtronic) in relatively simple lesions. Methods and Results: 117 patients (125 lesions) with single de novo lesion of a native coronary artery ��� 2.5 to ��� 4 mm in diameter, lesion ��� 20 mm in length who underwent elective stent implantation were enrolled. Patients were randomized to either SES (n=60), or CTSS (n=65). Six-month angiographic and clinical results were compared. There were no differences in baseline characteristics between the 2 groups. Up to now, angiographic follow-up rate was 50% and 54% in SES and CTSS group respectively (p=NS) (further follow-up data will be available until the conference). Mean target vessel reference diameter (2.8 mm vs. 3.0 mm, p=NS) and mean lesion length (16.6 mm vs. 17.9 mm, p=NS) were not different in SES and CTSS group respectively. Stent length was longer in SES group (22.3 mm vs. 18.5 mm, p<0.01). Percent stenosis (18.6% vs. 34.6 %, p<0.05) and late loss (0.31 mm vs. 0.95 mm, p<0.01) of the stented segments were lower in SES group than the CTSS group. In-lesion binary restenosis rate was also lower in SES group (4.9% vs. 21.3%, p<0.01). Up to now, six month clinical follow-up results were available in 68% and 72% in SES and CTSS group respectively. There was no death or myocardial infarction in both groups. The target lesion revascularization was occurred in one patient of DES group and three patients of CTSS group that tended toward a correlation (3.3% vs. 8.6%, p=NS). Conclusion: In relatively simple lesions, SES seems to have better angiographic and clinical results than CTSS.