This study examined the effects of a 12-week aerobic exercise program on psychological well-being and cognitive functioning in a group of ethnically diverse older adults living in an urban community. Forty-eight older men and women (mean age = 72 +/- 6) were randomly assigned to one of three groups: an aerobic exercise training group, a social activity control group, or a waiting list group. Results indicated little change in psychological well-being and provided limited support for the association of physiological improvement with enhanced mastery and cognitive functioning.