OBJECTIVE: To provide a broad picture of the costs of obesity using data from the US and major European countries. METHOD: Literature (2000-2004) was searched via Medline using cost keywords: cost, cost-effectiveness, cost-benefit, cost-efficiency. Selected citations were reviewed by title and abstract, followed by retrieval of relevant articles, review and synthesis of cost information. RESULT: Direct medical expenditures for obesity in the US were estimated to be between $70-$94 billion and $331 billion – with all obesity associated comorbidities included. This represented approximately 5.7%-9.4% of the adult direct health spending. Cardiovascular disease and diabetes constituted approximately 70% of the obesity-related cost. Indirect costs associated with obesity were estimated to be at least $48 billion. The expected mean costs for persons with BMI=30-34 and BMI=35-39 were 12% and 19% higher (respectively) than persons with BMI<25. Women spent more than men for obesity care. In the US, Wyoming showed the lowest expenditure for obesity ($87 million), and California the highest ($7.7 billion). Direct costs of obesity in Europe were estimated between 1.5% and 4% of total health expenditures, with the UK, Germany and France all showing similar expenditures (1.5%). Expenses associated with comorbid hypertension, coronary heart disease and diabetes were the main drivers of cost in the UK (80.5%). Indirect costs in the UK were estimated at £2.1 billion, of which £1.3 billion (61%) was due to work loss. Drug interventions using Orlistat, Sibutramine and Metformin were all cost-effective with the cost per QALY gained ranging between $8,327 to $19,968 (?4,780 to ?45,881). CONCLUSION: The costs attributable to obesity in both the US and Europe represented a significant portion of the national health expenditure for those countries reviewed, with comorbid cardiovascular disease and diabetes constituting the major components of obsesity associated health care costs.