Recent years have seen a dramatic rise in the prevalence of obesity in many countries, stimulating interest in the health and economic consequences of this phenomenon. In this article, we provide a systematic review of the literature on the medical-care cost burden of obesity. Relevant studies were identified using a computerized search of the medical literature for English-language articles published between 1990 and 2001. The 18 studies that met all criteria for inclusion in the review can be classified as modelling or database studies and further distinguished as cross-sectional or longitudinal in nature. The majority of studies that have been conducted are cross-sectional modelling studies, including 10 studies reporting the burden of obesity to national health systems. These suggest that obesity accounts for 5.5-7.0% of national health expenditures in the United States and 2.0-3.5% in other countries for which estimates have been reported. Other studies highlight the burden of obesity from other perspectives, including employers and health plans, as well as the impact of obesity on future disease risks and associated medical-care costs. Despite various methodological limitations, discussed herein, this body of research leads to the inescapable conclusion that obesity exacts an immense economic toll in various countries throughout the world.