Leisure-time physical activity enhances health and functioning in older populations. However, few data are available on the correlation between self-reported leisure-time physical activity and cardiorespiratory fitness in the elderly. Treadmill exercise testing results were obtained for 1,006 members (median age 67 years) of a community-based sample. Subjects completed a standardized evaluation of medical/social history and measures of physical function. Leisure-time physical activity in the 12 months and 7 days before interview and over subjects' lifetimes was summarized as total and activity-specific METs/week and [METs * (hours/week)]. Multiple linear regression was used to investigate the cross-sectional, sex-specific associations between peak oxygen consumption (VO2) and exercise duration. After adjustment for age, body mass index, smoking history, medical morbidity, direct measures of physical functioning, forced expiratory volumes, and maximum respiratory muscle pressure, leisure-time physical activity accounted for < or = 5% of the variance of VO2 and exercise duration. Results were unchanged when analyses were restricted to subjects who achieved high levels of exercise. These data indicate that measures of aerobic capacity cannot be used to "validate" self-reported leisure-time physical activity in older subjects, and they further suggest that beneficial effects of physical activity in the elderly are the result of metabolic effects that are not reflected well by maximal aerobic capacity during exercise testing.