The CIDI is a fully standardised diagnostic interview designed for assessing mental disorders based on the definitions and criteria of ICD-10 and DSM-III-R. Field trials with the CIDI have been conducted in 18 centres around the world, to test the feasibility and reliability of the CIDI in different cultures and settings, as well as to test the inter-rater agreement for the different types of questions used. Of 590 subjects interviewed across all sites and rated by an interviewer and observer, 575 were eligible for analysis. The CIDI was judged to be acceptable for most subjects and was appropriate for use in different kinds of settings. Many subjects fulfilled criteria for more than one diagnosis (lifetime and six-month). The most frequent lifetime disorders were generalised anxiety, major depression, tobacco use disorders, and agoraphobia. Percentage agreements for all diagnoses were above 90% and the kappa values were all highly significant. No significant numbers of diagnostic disconcordances were found with lifetime, six-month, and four-week time frames.