This paper outlines the principal aims and design of the German National Health Interview and Examination Survey, mental health supplement (GHS-MHS), the first nationwide, epidemiological study of both somatic and mental health in Germany on a representative sample of 4,181 subjects in the community. Both the broader context of the study--in particular its methodological relation to the social and somatic core survey of the German National Health Interview and Examination Survey (GHS-CS)--and the internal methodology of the mental health supplement (GHS-MHS) are presented. The study's strategies and method are derived from a consideration of important theoretical issues arising from epidemiological studies in the field of public health. The main instrument used to assess diagnoses of mental disorders was a standardized diagnostic interview for mental disorders (following DSM-IV (CIDI)) applied by clinically trained interviewers. This diagnostic interview was supplemented by modules on comorbidity, help seeking, treatment and impairment. Somatic health diagnoses were made using an integrated approach including self-report measures, a standardized clinical interview, and laboratory measures. Findings on sampling, response rate, weighting and sample characteristics are presented. Critical issues are discussed, including the scientific objectives that have been achieved by the study. Overall, the GHS core survey and its mental health supplement provide the mental health research community with complex data that allow for high-quality analysis of mental disorders and associations with somatic disorders.