Abstract： Background::The development of the technique has improved the success rate of percutaneous coronary intervention (PCI) for instent chronic total occlusion (IS-CTO). However, long-term outcomes remain unclear. The present study sought to investigate long-term outcomes of PCI for IS-CTO.Methods::A total of 474 IS-CTO patients were enrolled at two cardiac centers from 2015 to 2018 retrospectively. These patients were allocated into either successful or failed IS-CTO PCI groups. The primary endpoint (major adverse cardiac events [MACE]) consisted of recurrent angina pectoris (RAP), target-vessel myocardial infarction (MI), heart failure, cardiac death, or ischemia-driven target-vessel revascularization (TVR) at follow-up. Multivariable Cox regression analysis was used to investigate the association between treatment appropriateness and clinical outcomes.Results::A total of 367 patients were successfully treated with IS-CTO PCI while 107 patients had failed recanalization. After a median follow-up of 30 months (interquartile range: 17-42 months), no significant difference was observed between the two groups for the following parameters: cardiac death (successful PCI vs. failed PCI: 0.9% vs. 2.7%; adjusted hazard ratio [HR]: 1.442; 95% confidence interval [CI]: 0.21-9.887; P = 0.709), RAP (successful PCI vs. failed PCI: 40.8% vs. 40.0%; adjusted HR: 1.025; 95% CI: 0.683-1.538; P = 0.905), heart failure (successful PCI vs. failed PCI: 6.1% vs. 2.7%; adjusted HR: 0.281; 95% CI: 0.065-1.206; P = 0.088), target-vessel related MI (successful PCI vs. failed PCI: 1.5% vs. 2.7%; adjusted HR: 1.150; 95% CI: 0.221-5.995; P = 0.868), MACE (successful PCI vs. failed PCI: 44.2% vs. 45.3%; adjusted HR: 1.052; 95% CI: 0.717-1.543; P = 0.797). More patients were free of angina in the successful IS-CTO PCI group compared with failed PCI in the first (80.4% vs. 60%, P < 0.01) and second years (73.3% vs. 60.0%, P = 0.02) following up. Successful IS-CTO PCI had a lower incidence of MACE in the first and second years (20.2% vs. 40.0%, P < 0.01; 27.9% vs. 41.3%, P = 0.023) compared with failed PCI. After a median follow-up of 30 months, the reocclusion rate was 28.5% and TVR was 26.1% in the successful IS-CTO PCI group. Receiving >18 months of dual antiplatelet therapy (DAPT) was an independent predictor of decreased risk of TVR (HR: 2.682; 95% CI: 1.295-5.578; P = 0.008) or MACE (without TVR) (HR: 1.898; 95% CI: 1.036-3.479; P = 0.038) in successful IS-CTO PCI. Conclusions::After a median follow-up of 30 months, the successful IS-CTO PCI group had MACE similar to that of the failed PCI group. However, the successful IS-CTO PCI group had improved angina symptoms and were free from requiring coronary artery bypass grafting in the first or second years. To decrease MACE, DAPT was found to be essential and recommended for at least 18 months for IS-CTO PCI.