OBJECTIVES: The objective of this study was to estimate the existing financial costs from obesity in the United Kingdom (UK). METHODS: This comprehensive study was undertaken using a number of data sources that included a measure of height and weight. Population data were taken from published UK governmental sources. NHS hospital utilisation data from a region, in addition to corresponding specialized survey data (Health outcomes data repository [HODaR]). Cost data were taken from statistical governmental series and published sources (HRGs). Estimates of financial cost - including direct, indirect and intangible costs – were available from HODaR. All costs for all disease categories were calculated for different groups defined by age, sex and body mass index (BMI). Resulting values in alternative categories were compared using the Mann-Whitney U test, comparing overweight and obese patients with ‘normal' groups. Provided the test indicated a significant difference to the normal group, the amount of additional costs was calculated and termed excess costs. Prices are in UK£, 2002. Unusually, this considered all diseases including those where obesity provides a protective affect e.g., osteoporosis. RESULTS: In UK in 2002 approximately 10.5 million adults age >18 years were obese (BMI >30 kg/m²), equivalent to 22.9% of the population. Total direct excess costs were estimated as £1.5 billion. Proportionally, the most costly excess cost category occurred in the provision of social services. The indirect costs due to work loss in the 18–54 year-old group accounted for £2.7 billion. The marginal excess costs accounted for 2.3% of the total NHS budget. Furthermore, quality of life was significantly lower in obese people. CONCLUSIONS: These results confirm the current heavy financial toll of obesity in the UK. Obesity is already a major health problem in the UK and if recent trends of increasing BMI continue it will intensify.