The International Classification of Disease (ICD-10) produced by the World Health Organization in 1993 distinguishes between etiology, pathology and manifestations of disease but is based principally on etiology. The International Classification of Impairments, Disabilities and Handicaps (ICIDH, 1980) is partly based on the ICD but differs from it in several respects. It recognizes impairment as an exteriorized loss of structure, or abnormality of function at the organ level, disability as a restriction of actions at the person level and handicap as a set of disadvantages within the individual''s particular social context. Thus, three different levels are involved with, in most cases, impairment leading to disability and disability leading to handicap. These distinctions are relevant to stroke outcome research, in which so-called stroke scales are used to quantify neurological impairments while disabilities are usually assessed in terms of activities of daily living. Handicap is more difficult to measure and is rarely analyzed in stroke outcome research. With progressively higher levels of assessment, from impairment to handicap, the essential elementary variable, i.e. infarct size, becomes a weaker predictor of the patient''s outcome because more and more other variables contribute to the changes observed at each ascending hierarchical level.