With over half of the US population currently overweight and 31% of adults now obese, the primary care setting may represent an important source of weight-loss support, in the interest of cardiovascular prevention. Yet, although the US Preventive Services task force recommends that physicians screen all adult patients for obesity and offer intensive counseling and behavioral interventions to promote sustained weight loss for obese adults, the recommendation has not been widely implemented. The Internet may help overcome many of the barriers that have prevented intensive obesity counseling in the clinical setting. The aim of this study is to examine whether Internet-based interventions for developing healthier lifestyles can improve preventive health care in a cost-effective manner.