Patient-reported outcomes (PROs) provide intrinsic knowledge about a patient's health, functional status, symptoms, treatment preferences, satisfaction, and quality of life. They have become an established approach for assessing health outcomes. The Health Assessment Questionnaire (HAQ), introduced in 1980, is among the first PRO instruments designed to represent a model of patient-oriented outcome assessment. The HAQ is based on five patient-centered dimensions: disability, pain, medication effects, costs of care, and mortality. It has been validated by mail, in the office, by telephone, and by comparison with paraprofessional and physician judgments as a reliable instrument, and has been significantly correlated with other PRO instruments. Typically, one of two HAQ versions is used: the Full HAQ, which assesses all five dimensions, and the Short or 2-page HAQ, which contains only the HAQ disability index (HAQ-DI) and the HAQ's patient global and pain visual analog scales (VAS). The HAQ-DI and the global and pain VAS (i.e., the short HAQ) have essentially retained their original content since their inception, while the Full HAQ undergoes periodic revision to address issues of contemporary scientific interest. The HAQ-DI has been translated or culturally adapted into more than 60 different languages or dialects and has become part of the National Institutes of Health "Road-map" Project, the Patient-Reported Outcomes Measurement Information System (PROMIS).