Estimation of the prevalence and secular trends in paediatric obesity in Europe is impeded by methodological problems in the definition of obesity and the paucity of data sets that mirror the demographic, cultural and socioeconomic composition of the European population. The available prevalence data show that paediatric obesity is increasing throughout Europe but the patterns vary with time, age, sex and geographical region. The highest rates of obesity are observed in eastern and southern European countries. Even within countries there may be marked variability in the rates of obesity. It is unclear whether these trends are a simple consequence of an overall increase in fatness in Europe or whether there may be sub-groups of children who, at certain ages, are either particularly susceptible to environmental challenges or are selectively exposed to such challenges. In addition to the general increase in adiposity in European youth, there is also evidence of an increasing degree of obesity, particularly in older children and adolescents. No definite conclusions can be made about the respective contribution of energy intake and physical activity to the increasing prevalence of obesity. Changing demographic and social circumstances are linked to childhood obesity but it is highly unlikely that these interact in similar ways in the genesis of obesity in different individuals and population groups. In conclusion, the limited understanding of the variability in susceptibility to obesity in European youth provides powerful justification for the development of preventive strategies which are population based rather than selectively targeted at high-risk children.