Postoperative pulmonary complications are as frequent and clinically important as cardiac complications in terms of morbidity, mortality, and length of stay. However, there has been much less research and no previous systematic reviews of the evidence of interventions to prevent pulmonary complications. To systematically review the literature on interventions to prevent postoperative pulmonary complications after noncardiothoracic surgery. MEDLINE English-language literature search, 1 January 1980 through 30 June 2005, plus bibliographies of retrieved publications. Randomized, controlled trials (RCTs); systematic reviews; or meta-analyses that met predefined inclusion criteria. Using standardized forms, the authors abstracted data on study methods, quality, intervention and control groups, patient characteristics, surgery, postoperative pulmonary complications, and adverse events. The authors qualitatively synthesized, without meta-analysis, evidence from eligible studies. Good evidence (2 systematic reviews, 5 additional RCTs) indicates that lung expansion interventions (for example, incentive spirometry, deep breathing exercises, and continuous positive airway pressure) reduce pulmonary risk. Fair evidence suggests that selective, rather than routine, use of nasogastric tubes after abdominal surgery (2 meta-analyses) and short-acting rather than long-acting intraoperative neuromuscular blocking agents (1 RCT) reduce risk. The evidence is conflicting or insufficient for preoperative smoking cessation (1 RCT), epidural anesthesia (2 meta-analyses), epidural analgesia (6 RCTs, 1 meta-analysis), and laparoscopic (vs. open) operations (1 systematic review, 1 meta-analysis, 2 additional RCTs), although laparoscopic operations reduce pain and pulmonary compromise as measured by spirometry. While malnutrition is associated with increased pulmonary risk, routine total enteral or parenteral nutrition does not reduce risk (1 meta-analysis, 3 additional RCTs). Enteral formulations designed to improve immune status (immunonutrition) may prevent postoperative pneumonia (1 meta-analysis, 1 additional RCT). The overall quality of the literature was fair: Ten of 20 RCTs and 6 of 11 systematic reviews were good quality. Few interventions have been shown to clearly or possibly reduce postoperative pulmonary complications.