The assessment of disability prevalence in populations is a long-standing concern. In the mid-1970s the World Health Organization (WHO) introduced a scheme for the measurement of the consequences of disease. The classification of the long-term non-fatal consequences of disease is structured on three axes, corresponding roughly to experiences at the level of organ or function (impairment--1009 items), individual action (disability--338 items) and societal interaction (handicap/disadvantage--72 items). The International Classification of Impairments, Disabilities, and Handicaps (ICIDH) is now well established. This paper describes developments in the use of the ICIDH since 1980, in assessing the prevalence of disability in populations, in formulating policy decisions, in management at institution level, and in the care of individuals. It lists problems identified in the use of the ICIDH, such as the need to clarify the role and interrelationship of environmental factors in the definition and development of the different planes addressed by the ICIDH, problems of overlap between disabilities and handicaps, and between impairments and disabilities. Suggestions for improvement include a greater emphasis on presenting handicap as a description of the interrelation between impairments or disabilities and their physical and social environment. It is anticipated that a revised proposal will be finalized for 1998 and formally issued in 1999.