Obesity is now being considered a rapid growing economic burden on the healthcare system of many countries. These costs should include expenditure on prevention, as well as the investigation and treatment of obesity and its related problems. Accurate information on the cost of obesity in Hong Kong is lacking so we analysed the annual hospital discharges in a representative district hospital in Hong Kong. The estimated hospitalization costs in Hong Kong' public hospitals were HK$ 2.29 billion (US$ 0.29 billion) in 1998 and HK$ 3.36 billion (US$ 0.43 billion) in 2002 accounting for 8.2–9.8% of total public expenditure on health in Hong Kong. Based on the likelihood ratio of diabetes, hypertension and dylsipidaemia related to obesity in Hong Kong Chinese (defined as body mass index ≥25 kg m−2) the estimated proportion of these conditions attributable to obesity are 10–20%. In addition, significant amounts of money are being spent by the public on obesity self management schemes of no proven benefit. In 2005, 5.5% of Hong Kong's total population was consuming proprietary drugs for obesity or its related conditions. To properly assess the overall costs of obesity, other indirect costs should also be considered such as economic losses on sick leave because of obesity and its related conditions.