The prevalence of asthma, lung self-efficacy beliefs, physical activities, and physical fitness of adolescent girls were studied in a private inner-city high school serving a multiethnic, middle-class population using a questionnaire, a test of physical fitness, and an activity log. Twenty-two percent of the 172 girls were diagnosed with asthma, and an additional 15% of the girls experienced breathing difficulties. It was found that asthmatic girls were less physically fit, reported lower self-efficacy regarding their lung functioning during vigorous activities, and participated less often in those activities than nonasthmatic girls. Perceived lung efficacy was found to predict girls' subsequent participation in physical activities significantly, even when the effects of asthma, smoking, and physical fitness were controlled statistically.