Purpose: To perform a meta-analysis of effectiveness and adverse events associated with surgical treatment of obesity.

Data Sources: MEDLINE, EMBASE, Cochrane Controlled Trials Register, and systematic reviews. Study Selection: Randomized, controlled trials; observational studies; and case series reporting on surgical treatment of obesity.

Data Extraction: Information about study design, procedure, population, comorbid conditions, and adverse events.

Data Synthesis: The authors assessed 147 studies. Of these, 89 contributed to the weight loss analysis, 134 contributed to the mortality analysis, and 128 contributed to the complications analysis. The authors identified 1 large, matched cohort analysis that reported greater weight loss with surgery than with medical treatment in individuals with an average body mass index (BMI) of 40 kg/m(2) or greater. Surgery resulted in a weight loss of 20 to 30 kg, which was maintained for up to 10 years and was accompanied by improvements in some comorbid conditions. For BMIs of 35 to 39 kg/m(2), data from case series strongly support superiority of surgery but cannot be considered conclusive. Gastric bypass procedures result in more weight loss than gastroplasty. Bariatric procedures in current use (gastric bypass, laparoscopic adjustable gastric band, vertical banded gastroplasty, and biliopancreatic diversion and switch) have been performed with an overall mortality rate of less than 1%. Adverse events occur in about 20% of cases. A laparoscopic approach results in fewer wound complications than an open approach.

Limitations: only a few controlled trials were available for analysis. Heterogeneity was seen among studies, and publication bias is possible.

Conclusions: Surgery is more effective than nonsurgical treatment for weight loss and control of some comorbid conditions in patients with a BMI of 40 kg/m(2) or greater. More data are needed to determine the efficacy of surgery relative to nonsurgical therapy for less severely obese people. Procedures differ in efficacy and incidence of complications.