A migration-specific approach was used in the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) and thus it was possible for the first time to include children with a migration background in a nationwide health survey in Germany in a number corresponding to their percentage of the population. This article presents the migration-specific approach used in KiGGS as well as a definition of the term "migrant" and its operationalisation. In addition, we analyse the representativity of the migrant subsample and present data on its composition. Altogether 2,590 children and adolescents with a migration background (both parents) took part in the study; in the weighted sample they account for 17.1% of all children and adolescents. Another 8.3% of the children and adolescents have one parent with a migration background. The two largest groups among the migrant children are Germans from Russia (29.9%) and children and adolescents of Turkish origin (28.2%). There are differences between migrants and non-migrants related to socio-economic status and place of living (rural/urban and East/West). Analyses of the representativity of the migrant sample show that children and adolescents with a lower level of education are under-represented, whereas there were no differences with regard to sex, the fathers' occupation or the mothers' smoking status. Non-respondents rate their children's health better than respondents. Since the successful integration of children and adolescents with a migration background into the KiGGS study brings with it a sufficiently large number of cases and since KiGGS covers a wide range of health-related topics, comprehensive migration-specific analyses can be performed. Thus, KiGGS will contribute to filling some of the current gaps in our knowledge of migrant children's health.