This paper shows the trends in the prevalence of overweight (body mass index [BMI] >or= 25 kg m-2) and obesity (BMI >or= 30 kg m-2) in the Netherlands. Overweight (obesity) prevalence in adult males increased from 37% (4%) in 1981 to 51% (10%) in 2004, and in adult females from 30% (6%) in 1981 to 42% (12%) in 2004, according to self-reported data. In boys and girls, obesity prevalence doubled or even tripled from 1980 to 1997, and again from 1997 to 2002-2004 a two- or threefold increase was seen for almost all ages. According to the most recent data, overweight (obesity) prevalence figures range, depending on age, from 9.2% to 17.3% (2.5-4.3%) in boys, and from 14.6% to 24.6% (2.3-6.5%) in girls. There is a lack of data on the national prevalence of overweight and obesity based on measured height and weight and on prevalences in different subgroups of the population. Regular national representative health examination surveys that measure height and weight are needed to assess the prevalence of overweight and obesity and its distribution over subgroups in the population, and to properly direct and evaluate prevention activities.