In the last decade, the prevalence of obesity has increased significantly in populations worldwide. A less dramatic, but equally important increase has been seen in our knowledge of its effects on health and the burden it places on healthcare systems. This systematic review aims to assess the current published literature on the direct costs associated with obesity. A computerized search of English language articles published between 1990 and June 2009 yielded 32 articles suitable for review. Based on these articles, obesity was estimated to account for between 0.7% and 2.8% of a country's total healthcare expenditures. Furthermore, obese individuals were found to have medical costs that were approximately 30% greater than their normal weight peers. Although variations in inclusion/exclusion criteria, reporting methods and included costs varied widely between the studies, a lack of examination of how and why the excess costs were being accrued appeared to be a commonality between most studies. Accordingly, future studies must better explore how costs accrue among obese populations, in order to best facilitate health and social policy interventions.