Population-based surveillance of health-related quality of life (HRQOL) is needed to promote the health and quality of life of U.S. residents and to monitor progress in achieving the two overall Healthy People 2010 goals: 1) increase the quality and years of healthy life and 2) eliminate health disparities. This report examines surveillance-based HRQOL data from 1993 through 2002. Survey data from a validated set of HRQOL measures (CDC HRQOL-4) were analyzed for 1993-2001 from the Behavioral Risk Factor Surveillance System (BRFSS) surveys for the 50 states and the District of Columbia (DC) and for 2001-2002 from the National Health and Nutrition Examination Survey (NHANES). These measures assessed self-rated health; physically unhealthy days (i.e., the number of days during the preceding 30 days for which physical health, including physical illness and injury, was not good); mentally unhealthy days (i.e., the number of days during the preceding 30 days for which mental health, including stress, depression, and problems with emotions, was not good); and days with activity limitation (i.e., number of days during the preceding 30 days that poor physical or mental health prevented normal daily activities). A summary measure of overall unhealthy days also was computed from the sum of a respondent's physically unhealthy and mentally unhealthy days, with a maximum of 30 days. During 1993-2001, the mean number of physically unhealthy days, mentally unhealthy days, overall unhealthy days, and activity limitation days was higher after 1997 than before 1997. During 1993-1997, the percentage of respondents with zero overall unhealthy days was stable (51%-53%) but declined to 48% by 2001. The percentage of respondents with >/=14 overall unhealthy days increased from 15%-16% during 1993-1997 to 18% by 2001. Adults increasingly rated their health as fair or poor and decreasingly rated it as excellent or very good. Women, American Indians/Alaska Natives, persons of "other races," separated or divorced persons, unmarried couples, unemployed persons, those unable to work, those with a <$15,000 annual household income, and those with less than a high school education reported worse HRQOL (i.e., physically unhealthy days, mentally unhealthy days, overall unhealthy days, and activity limitation days). Older adults reported more physically unhealthy days and activity limitation days, whereas younger adults reported more mentally unhealthy days. A seasonal pattern was observed in physically unhealthy days and overall unhealthy days. During 1993-2001, BRFSS respondents in 13 states reported increasing physically unhealthy days; respondents in 13 states and DC reported increasing mentally unhealthy days; respondents in Alabama, Connecticut, Maine, New Jersey, New Mexico, North Carolina, and Oregon reported both increasing physically and mentally unhealthy days; and respondents in 16 states and DC reported increasing activity limitation days. During 2001-2002, NHANES respondents with one or more medical conditions (e.g., arthritis or stroke) reported worse HRQOL than those without such conditions, and those with an increasing number of medical conditions reported increasingly worse HRQOL. Policy makers and researchers should continue to monitor HRQOL and its correlates in the U.S. population. In addition, public health professionals should expand monitoring to populations currently missed by existing surveys, including institutionalized and homeless persons, adolescents, and children. A key aspect is to study and identify the personal and community determinants of HRQOL in prevention research and population studies, to understand how to improve HRQOL, and to reduce HRQOL disparities. In addition, population health assessment professionals should continue to refine and validate HRQOL, functional status, and self-reported health measures.