The Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) includes in Chapter V a detailed classification of over 300 mental and behavioural disorders. Its publication follows extensive field-testing by more than 100 clinical and research centres in 40 countries. There are two main versions available: Clinical Descriptions and Diagnostic Guidelines and Diagnostic Criteria for Research. The former provides clinical descriptions detailing the principal signs and symptoms of each disorder, together with other important but less specific associated features, as well as comprehensive guidelines for their diagnosis. The latter version is intended to help those researching specific disorders to maximize the homogeneity of study groups. To this end, it sets out criteria that allow the selection of individuals with clearly similar symptoms and other characteristics