The Functional Assessment of Chronic Illness Therapy (FACIT) Measurement System is a collection of health-related quality of life (HRQOL) questionnaires targeted to the management of chronic illness. The measurement system, under development since 1987, began with the creation of a generic CORE questionnaire called the Functional Assessment of Cancer Therapy-General (FACT-G). The FACT-G (now in Version 4) is a 27-item compilation of general questions divided into four primary QOL domains: Physical Well-Being, Social/Family Well-Being, Emotional Well-Being, and Functional Well-Being. It is appropriate for use with patients with any form of cancer, and extensions of it have been used and validated in other chronic illness condition (e.g., HIV/AIDS; multiple sclerosis; Parkinson's disease; rheumatoid arthritis), and in the general population. The FACIT Measurement System now includes over 400 questions, some of which have been translated into more than 45 languages. Assessment of any one patient is tailored so that the most-relevant questions are asked and administration time for any one assessment is usually less than 15 minutes. This is accomplished both by the use of specific subscales for relevant domains of HRQOL, or computerized adaptive testing (CAT) of selected symptoms and functional areas. FACIT questionnaires can be administered by self-report (paper or computer) or interview (face-to-face or telephone). Available scoring, normative data and information on meaningful change now allow one to interpret results in the context of a growing literature base.