The Composite International Diagnostic Interview, or CIDI, is a fully structured interview that maps the symptoms elicited during the interview onto DSM-IV and ICD-10 diagnostic criteria and reports whether the diagnostic criteria are satisfied - nothing more, nothing less. The inter-rater reliability has been demonstrated to be excellent, the test-retest reliability good, and the validity has been demonstrated to be good, given the methodological constraints. The CIDI is available in lifetime and 12-month versions, and in both paper-and-pencil and computer-administered forms. The latter version is suitable for self-administration in cooperative subjects. The CIDI is available in many languages. It is supported by ten centres around the world, which conduct regular training programmes for interviewers. The training programmes are standardised and the training materials are comprehensive. The data from the CIDI is entered into standard data entry and scoring programmes that give as output the diagnostic criteria satisfied. The interviews, the training materials, and the scoring programmes are copyright by the World Health Organization (WHO) and are supervised by an advisory committee on behalf of WHO. That committee and the training centres welcome enquiries from researchers and clinicians who are interested in using the CIDI.