The practice of performing percutaneous coronary intervention (PCI) in centers without on-site cardiac surgical backup is controversial. Using data from facilities that participated in the American College of Cardiology/National Cardiovascular Data Registry, the incidence of PCI without on-site surgical backup was evaluated. From January 1, 2001 through December 31, 2004, 39 of 449 (8.7%) centers were identified as sites that performed PCI without on-site surgical backup. By the end of 2005, 75 of 463 (16%) participating facilities were performing PCI without on-site backup. By using standardized data element definitions, it was possible to differentiate between patients who underwent elective PCI and those who had urgent nonelective PCI for acute ST-segment elevation myocardial infarction or non-ST-segment elevation myocardial infarction. This analysis showed that the number of elective and nonelective PCI procedures with or without on-site surgical backup per quarter had increased significantly (p <0.0001) from 2001 to 2004. The number of PCI procedures performed without on-site surgical backup continued to increase in 2005. In conclusion, the significant increase in elective PCIs performed at facilities without on-site surgical backup occurred despite national guidelines that state elective PCI should not be done in centers without on-site cardiac surgery.