Obesity is a very common and an increasing nutritional problem in Finland and in other western countries and also in circumpolar areas. Dietary factors like high intakes of fat and alcohol, and physical inactivity predispose to obesity. Childhood obesity increases the risk of obesity in adulthood. Obesity is associated with cardiovascular diseases, non-insulin-dependent diabetes mellitus and musculoskeletal disorders which cause work disability. Prevention of obesity should be more focused because treatment of obesity is difficult and the long-term result generally poor. Multidisciplinary co-work is needed to find out how the factors of childhood are related to obesity in adulthood.