Introduction: Achieving stent optimization on intravascular ultrasound (IVUS) is associated with favorable clinical outcomes in new-generation drug-eluting stents (DESs) implantation. Little is known about the stent optimization criteria in lesion subsets assorted according to vessel size and lesion length. Hypothesis: We hypothesized lesion-specific IVUS criteria could provide a better prediction for the outcomes after DES implantation for diffuse coronary lesions. Methods: From four randomized trials comparing IVUS and angiography guidance in long coronary lesions, a total of 1,194 patients who underwent IVUS-guided intervention with DESs ≥26 mm in length were included. Primary endpoint was a major adverse cardiac event (MACE), defined as a composite of cardiovascular death, myocardial infarction, target vessel revascularization, or stent thrombosis at 1 year following intervention. Results: MACE occurred in 41 (3.4%) patients. Among possible combinations of absolute and relative expansion criteria, the combination best predicting MACE was minimal stent area (MSA) ≥5.4 mm 2 or 80% of mean lumen area (MLA) (Youden index=0.250) in overall patients. In 2x2 factorial subgroup analyses, the MSA cutoff was 4.9 mm 2 or 85% of MLA for shorter (<30 mm) lesions with a smaller vessel diameter (reference vessel diameter [RVD] <3.0 mm) (Index=0.616) and 5.6 mm 2 or 85% for shorter lesions with a larger vessel diameter (RVD ≥3.0 mm) (Index=0.211). In longer lesions (≥30 mm), the MSA cutoff was 5.5 mm 2 or 70% of MLA for smaller vessels (RVD <3.0 mm) (Index=0.469), and 6.2 mm 2 or 70% for larger vessels (RVD ≥3.0 mm) (Index=0.578). Conclusions: When IVUS is used to optimize DES implantations for long coronary stenoses, applying different criteria according to angiographic parameters might improve the outcomes. In relatively longer lesions with a larger vessel diameter, pursuing to achieve a higher absolute MSA value rather than relative expansion might be more important.