Although the prevalence of obesity in Sweden still is low in an international perspective, the development during the last decades is alarming in adults, adolescents and children alike. The prevalence of obesity [body mass index (BMI) > 30 kg m-2] in adults has doubled during the last two decades and is now approximately 10% in both men and women, according to estimates based on self-reported BMI from repeated random samples of the population. However, prevalence estimates based on measured BMI from the WHO MONICA study indicate that the self-reported data result in underestimates. In military conscripts, the prevalence of obesity (BMI > 30 kg m-2) almost quadrupled to 3.2% from 1971 to 1995, while the overweight fraction (BMI > 25 kg m-2) more than doubled to 16.3%. The development in younger age groups seems to be similar; the prevalence of overweight [International Obesity Task Force (IOTF)/Cole] in children aged 10 years in Gothenburg has doubled to 18% (2.9% obese) during the last decade, and similar figures have been reported in other studies. However, most reports on childhood overweight stem from the larger metropolitan areas, and hence may be underestimates because of the urban-rural influence on obesity-status. Recent data from non-urban areas in the northern part of Sweden estimate the prevalence of overweight (BMI > 20 kg m-2) in 10-year-olds to above 30%. In the most comprehensive study in children, including both rural and urban areas, BMI was measured among all children aged 10 years (n = 5517; 92.7% of the population) in the county of Ostergotland, and the prevalence of overweight (IOTF/Cole) was 22% in both boys and girls, of which 4% and 5% were obese respectively.