BACKGROUND AND METHODS: Obesity has become a problem of epidemic proportions in the U.S., with nearly two thirds of American adults being either overweight or obese. Current data suggest that this trend remains on the rise and threatens many of the gains that have been made in the prevention and treatment of heart disease. Exercise has long been considered an integral component of weight management, but available evidence suggests that exercise alone is a relatively inefficient means for losing weight. In contrast, regular exercise appears crucial in the prevention of weight gain and successful maintenance of weight loss, and in the fostering of cardiovascular health. This article reviews the available literature regarding the role of exercise in the prevention and treatment of obesity and evaluates the adequacy of current national guidelines.