The leading health status instruments in human immunodeficiency virus (HIV) research are based on the pool of items developed as part of the Medical Outcomes Study (MOS). The measures include the SF-20, MOS-HIV, SF-36, SF-12, SF-56, SF-38 (Patient Reported Status and Experience Survey (PARSE)), SF-21 and HIV Cost and Service Utilization Study (HCSUS) questionnaires. The instrument length ranges from 12 to 56 items, covering two to 11 dimensions. Completion requires from 2 to 14 minutes. Subscales are scored on a 0-100 scale (a higher score indicates better health); physical and mental health or overall summary scores are available for most of the measures. Three of the instruments are available in multiple languages. The instruments have been administered to over 20,000 persons with HIV in descriptive studies and clinical trials and there is substantial evidence for their reliability, construct and predictive validity and responsiveness. In several studies the measures have shown important differences between treatments. Although existing measures do not assess all domains relevant to HIV disease, additional subscales are available from the MOS pool. Some of the subscales may be prone to floor and ceiling effects. However, summary scales that encompass all of the subscales reduce this issue. Selection among MOS measures should be dictated by specific questions, the balance of available time and resources, and practical concerns.