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Mechanical small bowel obstruction (SBO) is a frequent indication for hospital admission. It is associated with significant morbidity and mortality and financial burden. The most common cause of SBO in medically underserved countries is hernia, but up to 70% of cases in the United States are due to adhesions.1 All patients who have had an operation in which the peritoneal cavity has been entered have a subsequent lifetime risk of obstruction secondary to adhesions. In an autopsy study of 752 cadavers, adhesions were found in 67% of those who had undergone a previous operation but in only 28% of cadavers with no previous operation.2 In a prospective analysis of 210 patients undergoing a laparotomy who had previously had one or more abdominal operations, 93% of patients had adhesions, compared with 10% of 115 patients who had asymptomatic adhesions at first-time laparotomy.3 The management of patients with acute SBO remains controversial. There are no uniform strategies regarding indications for or timing of operation. The decision to operate is at the discretion of the individual surgeon, but not based on high-quality evidence. Some surgeons support immediate operative management in almost all cases.4–7 However, studies on the natural history of adhesive obstructions have shown that more than 50% resolve with a conservative, nonoperative approach.8,9 Other surgeons use an initial nonoperative trial period of bowel decompression in stable patients without suspicion of bowel strangulation.10–14 As a result, the operative rates for SBO have been shown to vary widely, from 27% to 66%.15,16 The morbidity and mortality associated with operative management of SBO are recognized, but the responsible presurgical and intraoperative risk factors have not been identified. The Department of Veterans Affairs (VA) National Surgical Quality Improvement Program (NSQIP) was designed to overcome some of the limitations of retrospective analyses by prospectively gathering reliable, valid data about putative patient risk factors and outcomes of surgery in the VA healthcare system. These data are then used to construct mathematical models that report comparative risk-adjusted surgical morbidity and mortality rates. The initial National Veterans Affairs Surgical Risk Study that was conducted from October 1, 1991, through December 31, 1993, included 44 Veterans Affairs Medical Centers (VAMCs). The program was expanded on January 1, 1994, and now prospectively gathers data on surgical procedures performed at 123 VAMCs. There are more than 1 million entries to date. Each of these cases was selected according to defined criteria, assessed for 68 presurgical and 12 intraoperative variables judged likely to be predictors of complications and death, and monitored after surgery for 30-day mortality and for 21 specific and well-defined adverse outcomes. The reproducibility and accuracy of data collection have been demonstrated elsewhere.17–19 These data permit the construction of risk-prediction models using well-accepted statistical techniques.20 The present study uses these techniques to assess risk factors for morbidity and mortality following surgical treatment of SBO.