Although obesity traditionally has been considered a risk factor for coronary revascularization, recent data from registry studies have shown a possible protective effect of obesity on outcomes after percutaneous coronary intervention (PCI). Using data from the New York State Angioplasty database over a 4-year period, we analyzed 95,435 consecutive patients who underwent PCI. Classification of body mass index (BMI) was: underweight (<18.5 kg/m(2)), healthy weight (18.5 to 24.9 kg/m(2)), overweight (25 to 29.9 kg/m(2)), moderate obesity (class I) (30 to 34.9 kg/m(2)), severe obesity (class II) (35 to 39.9 kg/m(2)), and very severe obesity (class III) (>40 kg/m(2)). In-hospital postprocedural mortality and complications were compared among these groups. Compared with healthy weight patients, patient with class I or II obesity had lower in-hospital mortality and major adverse cardiac events (MACE) (combined death, myocardial infarction, and emergency surgery), whereas patients at the extremes of BMI (underweight and class III obese patients) had significantly higher mortality and MACE rates. Adjusted hazards ratios for in-hospital mortality according to BMI were: underweight (2.69), healthy weight (1.0), overweight (0.90), class I obese (0.74), class II obese (0.67), and class III obese (1.63). Patients at the extremes of BMI (<18.5 and >40 kg/m(2)) were at increased risk of MACEs, including mortality after PCI, whereas patients who were moderately to severely obese (BMIs 30 to 40 kg/m(2)) were at lower risk than healthy weight patients.