Asthma is a major contributor to impaired quality of life in the U.S. population. Little is known about population-based determinants of quality of life among people with asthma, however. Using data from the 2000 Behavioral Risk Factor Surveillance System, we examined the associations between selected sociodemographic, behavioral, and other determinants and quality of life among 12,111 participants with current asthma. In multiple logistical regression models, three variables--employment status, smoking status, and physical activity--were significantly associated with all measures of impaired quality of life (poor or fair health, > or = 14 physically unhealthy days, > 14 mentally unhealthy days, > or = 14 activity limitation days, or > or = 14 physically or mentally unhealthy days). Education was significantly and inversely related to impaired quality of life for all measures except activity limitation days. Men were less likely than women to report having > or = 14 physically unhealthy days, > or = 14 mentally unhealthy days, or > or = 14 physically or mentally unhealthy days. Compared with whites, Hispanics were more likely to report being in poor or fair health, and African Americans were less likely to report having > or = 14 physically unhealthy days or > or = 14 physically or mentally unhealthy days. In addition, participants with lower incomes were more likely to report impaired quality of life for three measures (general health status, > or = 14 physically unhealthy days, and activity limitation days). The heaviest participants were more likely to be in poor or fair health or to report having more > or = 14 physically unhealthy days, or > or = 14 physically or mentally unhealthy days. Insurance coverage and the time since their last routine checkup were not significantly associated with any of the quality-of-life measures. These results show that three potentially modifiable factors (smoking status, physical activity, body mass index) are associated with quality of life among persons with asthma. Furthermore, among people with asthma, the elderly, women, poorly educated, and low-income participants are especially likely to experience impaired quality of life.