Over the last 2 decades, assessment of patient health status has undergone a dramatic paradigm shift, evolving from a predominant reliance on biochemical and physical measurements to an emphasis upon health outcomes based on the patient's personal appreciation of their illness. The Health Assessment Questionnaire (HAQ), published in 1980, was among the first instruments based on patient centered dimensions. The HAQ was designed to represent a model of patient oriented outcome assessment and has played a major role in diverse areas such as prediction of successful aging, inversion of the therapeutic pyramid in rheumatoid arthritis (RA), quantification of nonsteroidal antiinflammatory drug gastropathy, development of risk factor models for osteoarthrosis, and examination of mortality risks in RA. The HAQ has established itself as a valuable, effective, and sensitive tool for measurement of health status. It has increased the credibility and use of validated self-report measurement techniques as a quantifiable set of hard data endpoints and has contributed to a new appreciation of outcome assessment. We review the development, content, and dissemination of the HAQ and provide reference sources for its uses, translations, and validations. We discuss contemporary issues regarding outcome assessment instruments relative to the HAQ's identity and utility. These include: (1) the issue of labeling instruments as generic versus disease-specific; (2) floor and ceiling effects in scales such as "disability"; (3) distances between values on scales; and (4) the continuing introduction of new measurement instruments and their potential effects.