Background: The objective was to compare patients with ischemic heart disease (IHD) undergoing percutaneous coronary intervention (PCI) who were included in randomized controlled trials (RCTs) (trial participants) with patients who were not included (nonparticipants) on a trial-by-trial basis and according to indication for PCI. Methods: In this cohort study, we compared patients with IHD who were randomized in RCTs in relation to undergoing PCI in Denmark between 2011 and 2015 were considered as RCT-participants in this study. The RCT-participants were compared with contemporary nonparticipants with IHD undergoing PCI in the same period, and they were identified using unselected national registry data. The primary end point was all-cause mortality. Results: A total of 10,317 (30%) patients were included in 10 relevant RCTs (trial participants), and a total of 23,644 (70%) contemporary patients did not participate (nonparticipants). In all the included RCTs, nonparticipants had higher hazard ratios for mortality compared to trial participants (P <.001). Among all patients treated with PCI, the pooled estimates showed a significantly higher mortality rate for nonparticipants compared to trial participants (hazard ratio: 2.03, 95% CI: 1.88-2.19) (P <.001). When patients were stratified according to indication for PCI, the pooled estimates showed a significantly lower mortality rate for trial participants compared to nonparticipants in all strata (P for all <.001). Conclusions: Trial participants in recently performed RCTs including patients undergoing PCI were not representative of the general population of patients with IHD treated with PCI according to clinical characteristics and mortality. The difference in mortality was found irrespective of the indication for PCI. Thus, results from RCTs including patients undergoing PCI should be extrapolated with caution to the general patient population.