The article describes the objectives and design of a prospective study of the prevalence, incidence and course of psychiatric disorders in a representative sample of non-institutionalized Dutch adults. A total of 7146 men and women aged 18–64, contacted through a multistage sample of municipalities and households, were interviewed at home in 1996. The primary diagnostic instrument was the CIDI, which determines the lifetime occurrence of DSM-III-R disorders. The disorders included were: mood disorders, anxiety disorders, eating disorders, schizophrenia and other non-affective psychotic disorders, and dependence and abuse of psychoactive substances. Follow-up measurements in the same sample were scheduled at 12 and 36 months. The net response to the first measurement was 69.7%. Poststratification weightings were applied for gender, age, marital status and degree of urbanization. Limitations and advantages of the study design are discussed. Findings are reported elsewhere in this issue.