In excess of 55% of adults in the United States are classified as either overweight (body mass index = 25-29.9 kg.m(-2)) or obese (body mass index > or = 30 kg.m(-2)). To address this significant public health problem, the American College of Sports Medicine recommends that the combination of reductions in energy intake and increases in energy expenditure, through structured exercise and other forms of physical activity, be a component of weight loss intervention programs. An energy deficit of 500-1000 kcal.d-1 achieved through reductions in total energy intake is recommended. Moreover, it appears that reducing dietary fat intake to <30% of total energy intake may facilitate weight loss by reducing total energy intake. Although there may be advantages to modifying protein and carbohydrate intake, the optimal doses of these macronutritents for weight loss have not been determined. Significant health benefits can be recognized with participation in a minimum of 150 min (2.5 h) of moderate intensity exercise per week, and overweight and obese adults should progressively increase to this initial exercise goal. However, there may be advantages to progressively increasing exercise to 200-300 min (3.3-5 h) of exercise per week, as recent scientific evidence indicates that this level of exercise facilitates the long-term maintenance of weight loss. The addition of resistance exercise to a weight loss intervention will increase strength and function but may not attenuate the loss of fat-free mass typically observed with reductions in total energy intake and loss of body weight. When medically indicated, pharmacotherapy may be used for weight loss, but pharmacotherapy appears to be most effective when used in combination with modifications of both eating and exercise behaviors. The American College of Sports Medicine recommends that the strategies outlined in this position paper be incorporated into interventions targeting weight loss and the prevention of weight regain for adults.