Background : Since several intravascular ultrasound studies (IVUS) have shown that optimal stent deployment is rarely achieved with angiographically guided angioplasty alone, stent postdilatation have become common practice and proven to be safe with bare metal stents. But postdilatation including high pressure may alter the local pharmacokinetics of drug eluting stent(DES) thus affect clinical and angiographic outcomes. Methods : Total 1795 patients were enrolled in this study from February 2003 to November 2004. Among them 1273 patients were postdilated after DES deployement. Their mean age was 62짹10(yrs) with M:F 1071:202. Among them 437 patients(34%) were diabetes, 717 patients(56%) presented with acute coronary syndrome(ACS). Results : Postdilated group had no difference in late loss, acute gain and MACE than non postdilated group in the entire cohort and CYPHER subgroup. There was no difference in TAXUS subgroup. When analyzed in diabetics, patients postdilated with high pressure(>12mmHg) had higher TLR rate(4.63 vs 9.62 p=0.0413) than postdilated with nominal pressure or non postdilated patients in the entire cohort. In subgroup analysis, TAXUS group with high pressure postdilatation, had significant higher TVR rate (4.65 vs 19.61 p=0.0052). The CYPHER group showed no significant differences. In contrast, in nondiabetics, there was no difference in TAXUS subgroup but significantly higher TVR and cardiac death in postdilated CYPHER group(8.16 vs 3.64 p=0.0461). In ACS patients, postdilated group showed larger follow up MLD and lower late loss. TLR/ TVR was significantly lower in postdilated group(8.18 vs 3.46 p=0.023). In CYPHER subgroup, postdilated patients with either nominal or high pressure, showed lower TLR/TVR rate(0.7 vs 4.2 p=0.0078, 0.73 vs 4.23 p=0.014) and lower all cause mortality (9.1 vs 3.3 p=0.0194) Conclusion : Postdilation increases TLR in diabetic patients depending on stent type. Postdilatation decreases late loss and TVR in nondiabetic patients depending on stent type. Postdilatation decreased TLR, TVR and all cause mortality in ACS group depending on stent type