The Mental Health Module (BELLA study) examines emotional well-being and behaviour in a representative sub-sample of 2,863 families with children aged 7 to 17 from the National Health Interview and Examination Survey for Children and Adolescents (KiGGS). The prevalence of mental health problems was determined using the Strengths and Difficulties Questionnaire (SDQ) and additional standardised screening measures. Of children and adolescents, 21.9 % (95 %CI: 19.9-24.0) showed signs of mental health problems. The psychiatric disorders observed included anxiety (10.0 %; 95 % CI: 8.7-11.6), conduct disorder (7.6 %; 95 % CI: 6.5-8.7) and depression (5.4 %; 95 % CI: 4.3-6.6). Of the risk factors examined, adverse family climate and low socioeconomic status stand out particularly as negative contributors. When several risk factors occur simultaneously, the prevalence of mental health problems increases markedly. Conversely, positive individual, family and social resources coincide with an absence of mental health problems. Children and adolescents with mental health problems display distinctly impaired health-related quality of life, and far from all of them are receiving treatment. Identifying high risk groups therefore requires the assessment of available resources in addition to the usual risk factors for mental and subjective health. Strengthening these resources should be a key objective, both in prevention and in interventions.