Patients with chronic renal insufficiency (RI) have higher in-hospital mortality and major adverse cardiac event (MACE) rates after percutaneous coronary intervention (PCI). The mechanisms of this adverse course are not well understood. It was hypothesized that this worse outcome may be caused by inadequate PCI results secondary to more complex coronary anatomy in patients with RI. Baseline, procedural, and outcome variables of all PCI cases at the University Health Network are entered prospectively in the PCI Registry. All PCI cases between April 1, 2000, and October 31, 2005, excluding patients in shock, who had preprocedural creatinine clearance (CrCl) measured were included in this study (n = 10,821 of 11,023 patients). Moderate RI (CrCl <60 ml/min) was evaluated as an independent predictor of procedural outcomes, death, and MACE (defined as death, myocardial infarction, abrupt closure, or coronary artery bypass grafting). Moderate RI (CrCl <60 ml/min) independently predicted the procedural outcomes of worse residual stenosis >20% (p = 0.03), number of undeliverable stents (p = 0.003), and smallest stent diameter (p <0.001). Worst residual stenosis >20% and any undeliverable stent were significantly associated with in-hospital MACEs (odds ratio [OR] 3.97, 95% confidence interval [CI] 3.0 to 5.3, p <0.001 and OR 1.89, 95% CI 1.2 to 2.9, p = 0.002) and mortality (OR 3.82, 95% CI 2.2 to 6.7, p <0.001 and OR 3.0, 95% CI 1.6 to 5.9, p = 0.002). These risks were independent of all other measured variables. In conclusion, moderate to severe RI was a strong predictor of worse procedural results during PCI, which, in turn, were independent predictors of in-hospital MACE and mortality and independent contributors to the higher risk of in-hospital adverse events observed after PCI in patients with RI.