BACKGROUND: The impact of OSA treatment with CPAP on percutaneous coronary intervention (PCI) outcomes remains largely unknown. METHODS: Between 2002 and 2012, we identified 390 patients with OSA who had undergone PCI. OSA was diagnosed through in-laboratory sleep studies and defined by an apnea-hypopnea index >= 5 events/h. The cohort was divided into three groups: (1) moderate-severe OSA successfully treated with CPAP (n = 128), (2) untreated moderate-severe OSA (n = 167), and (3) untreated mild OSA (n = 95). Main outcomes included repeat revascularization, major adverse cardiac events (MACEs) (ie, death, nonfatal myocardial infarction, repeat revascularization), and major adverse cardiac or cerebrovascular events (MACCEs). The median follow-up period was 4.8 years (interquartile range, 3.0-7.1). RESULTS: The untreated moderate-severe OSA group had a higher incidence of repeat revascularization than the treated moderate-severe OSA group (25.1% vs 14.1%, P = .019). There were no differences in mortality (P = .64), MACE (P = .33), and MACCE (P = .76) among the groups. In multivariate analysis adjusted for potential confounders, untreated moderate-severe OSA was associated with increased risk of repeat revascularization (hazard ratio, 2.13; 95% CI, 1.19-3.81; P = .011). CONCLUSIONS: Untreated moderate-severe OSA was independently associated with a significant increased risk of repeat revascularization aft er PCI. CPAP treatment reduced this risk.