The measurement of the long-term consequences of disease, which are said to affect 7-10% of the world population in both developing and developed areas, presents both technical and conceptual problems. The development of classification schemes, foremost among which is the International Classification of Impairments, Disabilities, and Handicaps (ICIDH), has considerably changed our perception of these consequences, and has influenced the areas of rehabilitation, social insurance and legislation, disability surveys and health planning. More indirect applications have been the use of classifications in identifying, at local level, disadvantages in everyday life and ways to mitigate these disadvantages; at the macroplanning level, the concept of disability-free life expectancy is gaining increasing recognition. There is an increasing call for revising and updating ICIDH, particularly in the area of handicap, where societal and environmental factors have to be more explicitly taken into account. The operationalization of proposed modifications will require considerable thought and discussion in which persons with disabilities and their representatives will have an important role to play.