Health care providers are under increasing pressure to lower costs by combining diagnostic and "ad hoc" interventional coronary procedures. Despite increasing use of such a treatment strategy, its effect on periprocedural safety has not been rigorously assessed in the current stent era. Using the 2000/2001 New York State Angioplasty Registry, we compared in-hospital clinical outcomes in 47,020 patients who underwent ad hoc percutaneous coronary interventions (PCIs) versus staged procedures. Patients with previous PCIs, acute myocardial infarction within 24 hours, thrombolytic therapy within 7 days, or those presenting with hemodynamic instability or shock were excluded. Patients in the staged intervention group were more likely to have hypertension, diabetes mellitus, peripheral vascular disease, previous stroke, heart failure, renal failure, previous coronary artery bypass grafting, and a lower left ventricular ejection fraction. Mortality rate (0.4% vs 0.4%, p = 0.299), major adverse cardiac events (0.7% vs 0.8%, p = 0.199), and incidence of renal failure/dialysis (0.1% vs 0.1%, p = 0.520) during in-hospital stay did not differ significantly between the ad hoc PCI and staged groups. There was a higher rate of access site injury in the staged cohort (0.4% vs 0.3%, p = 0.011), and this trend persisted after multivariate logistic regression analysis (odds ratio 1.34, 95% confidence interval 0.99 to 1.81, p = 0.061). In addition, patients with "high-risk" features had similar in-hospital clinical outcomes after either treatment approach. In conclusion, as currently practiced in New York State, the strategy of ad hoc PCI in selected patient cohorts appears to be as safe as the strategy of staged procedures.