Aerobic exercise is a common nonpharmacological intervention for the management of obesity. However, the efficacy of isolated aerobic exercise at promoting weight loss is unclear. We conducted a systematic review and meta-analysis to evaluate the efficacy of isolated aerobic exercise programs in overweight and obese populations. We searched for published randomized controlled trial reports of aerobic exercise through January 20, 2010. Trials with an isolated aerobic exercise intervention were included. A random-effect model was used to synthesize the results of each intervention. We identified 14 trials involving 1847 patients. The duration of aerobic exercise programs ranged from 12 weeks to 12 months. Results were pooled for programs with 6-month duration and programs with 12-month duration. Six-month programs were associated with a modest reduction in weight (weighted mean difference [WMD]=-1.6 kg; 95% confidence interval [CI], -1.64 to -1.56) and waist circumference (WMD=-2.12 cm; 95% CI, -2.81 to -1.44). Twelve-month programs also were associated with modest reductions in weight (WMD=-1.7 kg; 95% CI, -2.29 to -1.11) and waist circumference (WMD=-1.95 cm; 95% CI, -3.62 to -0.29). Moderate-intensity aerobic exercise programs of 6-12 months induce a modest reduction in weight and waist circumference in overweight and obese populations. Our results show that isolated aerobic exercise is not an effective weight loss therapy in these patients. Isolated aerobic exercise provides modest benefits to blood pressure and lipid levels and may still be an effective weight loss therapy in conjunction with diets. Copyright © 2011 Elsevier Inc. All rights reserved.