The International Classification of Diseases has, under various names, been for many decades the essential tool for national and international comparability in public health. This statistical tool has been customarily revised every 10 years in order to keep up with the advances of medicine. At first intended primarily for the classification of causes of death, its scope has been progressively widening to include coding and tabulation of causes of morbidity as well as medical record indexing and retrieval. The ability to exchange comparable data from region to region and from country to country, to allow comparison from one population to another and to permit study of diseases over long periods, is one of the strengths of the International Statistical Classification of Diseases, Injuries, and Causes of Death (ICD). WHO has been responsible for the organization, coordination and execution of activities related to ICD since 1948 (Sixth Revision of the ICD) and is now proceeding with the Tenth Revision. For the first time in its history the ICD will be based on an alphanumeric coding scheme and will have to function as a core classification from which a series of modules can be derived, each reaching a different degree of specificity and adapted to a particular specialty or type of user. It is proposed that the chapters on external causes of injury and poisoning, and factors influencing health status and contact with health services, which were supplementary classifications in ICD-9, should form an integral part of ICD-10. The title of ICD has been amended to "International Statistical Classification of Diseases and Related Health Problems"', but the abbreviation "ICD" will be retained.(ABSTRACT TRUNCATED AT 250 WORDS)