The purpose of this collection of papers is to describe the present state of development of Chapter V (F) of the Tenth Revision of the International Classification of Diseases (ICD-10) (to be published by the World Health Organization, Geneva), and to discuss some related issues concerning psychiatric classification in an international setting.

The proposals for the chapter dealing with mental, behavioural and developmental disorders in the tenth revision of the International Classification of Diseases (ICD) are in the true sense a product of many minds. In their development WHO has called on and received the generous advice and support of its network of collaborating centres, of the members of Expert Advisory Panels on Mental Health, Neurosciences and Drug Dependence and Alcohol Problems from some 60 countries, and of the non-governmental organizations with whom WHO is in official relations. Among the latter, the collaboration with the World Psychiatric Association has been particularly useful; this Association sent the text of the ICD to all of its member societies, assembled their views and comments and worked closely with WHO in incorporating these comments into the text of the ICD. The WPA has created a special committee under the chairmanship of Professor E. Stromgren which summarised all the views received, and maintained collaboration with WHO throughout the development of the proposals.

When Renaudin, aghast at the situation in 1856 wrote, “We now see anarchy in the field of classification threatening to split our ranks and robbing us of the victories of our predecessors”, he was not only providing an argument for adhering to a common system of communication in psychiatry, he was also stating why classifications are such an enchanting conundrum attracting attention, arousing emotion and giving rise to thought.

Against the background of impressive advances in the neurosciences, which are opening new perspectives on the mechanisms of mind, and the development of increasingly powerful instruments and methods with a potential to revolutionise clinical research in psychiatry, clinicians continue to disagree on the definition and taxonomy of the elementary units of observation in their universe of discourse: the individual mental disorders.

The discussion here is largely concerned with the purposes and structure of classifications of clinical concepts, variously called diseases, illnesses, disorders and syndromes, which are the main reasons why patients go to see doctors. Multiaspect (or multiaxial) classification has deservedly come to the fore in recent years, and seems likely to increase in importance for purposes of education, communication and research in the near future, but it is mentioned only briefly in the following discussion. The main focus of attention for the moment is the clinical descriptions of disorders; this is, of course, usually the first aspect in a multiaspect system, and the one around which the other aspects tend to be organised.

Classification is fundamental to science and a standard classification of diseases and injury is essential for the systematic statistical study of illness and death. This was recognised as early as the seventeenth century when such studies started and in 1853 Dr William Farr of London and Marc d'Espine of Geneva were entrusted with the task of preparing ‘a uniform nomenclature of causes of death applicable to all countries’. This led eventually to the International Statistical Classification of Diseases, Injuries and Causes of Death (ICD). In 1948, when the World Health Organization (WHO) was created, the newborn agency was asked to review and revise the classification regularly. The ICD is now undergoing its tenth revision.

This paper will review the major objectives and study design of the Field Trials of the draft chapter on Mental Behavioural and Developmental Disorders in the tenth revision of the International Classification of Diseases (ICD-10), now in preparation. The text used in this Field Trial is the Clinical Descriptions and Diagnostic Guidelines, which is more elaborate than the Short Glossary for this chapter that will be published in the main volume of ICD-10. The text for the former will be published together with the Diagnostic Criteria for Research and other parts of the WHO family of instruments relevant to mental health.

As work proceeds on the development of the Tenth Revision of the International Classification of Diseases (ICD-10) widespread interest has been expressed in the preparation of a multiaxial diagnostic schema for psychiatric patients. In consideration of this task, the present paper briefly notes pertinent international experience on multiaxial diagnosis, the discernible purposes of this approach, design requirements, and a specific multiaxial proposal.