The contribution of the BELLA study in filling the gap of knowledge on mental health and well-being in children and adolescents in Germany.

The mental health of children and adolescents is an epidemiological outcome of considerable public health relevance. This is because of a comparatively high prevalence of mental health problems and disorders in children and adolescents. The 'BELLA Study on Mental Health', a modular component of the Health Interview and Examination Survey for Children and Adolescents conducted by the Robert Koch-Institute, assessed the prevalence of general and specific mental health problems in a representative sample of children and adolescents in Germany. Furthermore, determinants of mental health were studied in a developmental context. In the cross-sectional part of the study, participants were interviewed to assess the occurrence of risk factors and available assets (protective factors) for mental health, providing valuable data for health monitoring and planning. The sample was also repeatedly studied in a 2-year longitudinal design in order to estimate the effect size of risk and protective factors for mental health, and to analyse their combined effects on the process of mental health development. The BELLA study--as described in this supplement--supplies valuable estimates of the prevalence of mental health problems and disorders, identifies risk groups needing intervention, and describes the subjective health of children and adolescents in Germany.