Background: Our aim was to determine the relationship between patient level characteristics and in-hospital postoperative complications among obese adults who underwent a bariatric procedure in New York state in 2003. Understanding patient level factors that predict or are associated with adverse outcomes among bariatric surgery patients can help to identify patients who need to be monitored particularly carefully. Methods: Using New York's inpatient discharge database, we identified adults who underwent a bariatric operation between January 1, 2003 and December 31, 2003 (n=7,868). Following preliminary descriptive analyses, a stepwise logistic regression model was constructed to identify significant patient level predictors of postoperative complications. Patient level risk factors included age, gender, race/ethnicity, and 24 co-morbid conditions. Results: 6.8% of adults undergoing a bariatric procedure in New York in 2003 experienced one or more of the postoperative complications included in the study. Respiratory complications were the most common type of complication, with >2% of patients experiencing pneumonia, collapsed lung, and/or respiratory complications secondary to the operation. Multivariate analyses by stepwise logistic regression identified age ≥50 years, male gender, Hispanic ethnicity, congestive heart failure, cardiac arrhythmia, other neurological disorders, and peptic ulcer as predictors of complications. Conclusions: Certain subpopulations of persons undergoing bariatric procedures may be at increased risk for adverse events and will need to be monitored carefully.