OBJECTIVE: Bariatric surgery is one of the fastest growing hospital procedures. Our objective is to examine the safety outcomes and utilization of resources in the 6 months after bariatric surgery using a nationwide, population-based sample. DATA/DESIGN: We examine insurance claims for 2522 bariatric surgeries, at 308 hospitals, among a population of 5.6 million nonelderly people covered by large employers in the 2001-2002 MarketScan data. Outcomes and costs were risk-adjusted using multivariate regression methods. PRINCIPAL FINDINGS: Although the complication rate was 21.9% during the initial surgical stay, the rate increased by 81% (P < 0.01) to 39.6% (95% confidence interval, 37.7-41.5%) over the 180 days after discharge. A total of 10.8% of the patients without 30-day complications developed a complication between 30 days and 180 days. Overall, 18.2% of the patients had some type of postoperative visit to the hospital with a complication (through readmission, outpatient hospital visit, or emergency room visit) within 180 days. Although there was no difference between men and women, the near-elderly had a 26% (P < 0.01) higher risk-adjusted complication rate than those age 18 to 39 years. Total 6-month risk-adjusted healthcare payments were $65,031 for those with 180-day readmissions compared with $27,125 for those without readmissions (P < 0.01). CONCLUSION: In contrast to current bariatric studies, which report a 20% in-hospital complication rate, we find a significantly higher complication rate over the 6 months after surgery, resulting in costly readmissions and emergency room visits. Thus, a clear way to reduce the costs and improve outcomes of bariatric surgery is to address the high rate of postoperative complications.