The German Health Interview and Examination Survey for Children and Adolescents (KiGGS) was conducted from May 2003 to May 2006 by the Robert Koch Institute in 167 communities representative of Germany. By collecting comprehensive and nationally representative data on the health status of children and adolescents aged 0 to 17 years, the study aimed to fill a longstanding evidence gap. Data from 17,641 study participants will be analysed in a timely and systematic manner by the Robert Koch Institute. Initially mainly descriptive analyses as presented in the current special issue on the KiGGS study, provide information on the distribution of main health characteristics according to sociodemographic key variables, including age, sex, region of residence (former East/West Germany), social status, and migrant background. We report here the rationale for a standard set of stratifying variables and the operationalisation of composite variables. Furthermore, we illustrate the public health relevance of the observed group differences using the example of an important health indicator: parents' evaluation of their children's general state of health.