A meta-analysis examined data from 36 studies linking physical activity to well-being in older adults without clinical disorders. The weighted mean-change effect size for treatment groups (d(C). = 0.24) was almost 3 times the mean for control groups (d(C). = 0.09). Aerobic training was most beneficial (d(C). = 0.29), and moderate intensity activity was the most beneficial activity level (d(C). = 0.34). Longer exercise duration was less beneficial for several types of well-being, though findings are inconclusive. Physical activity had the strongest effects on self-efficacy (d(C).= 0.38), and improvements in cardiovascular status, strength, and functional capacity were linked to well-being improvement overall. Social-cognitive theory is used to explain the effect of physical activity on well-being. ((c) 2005 APA, all rights reserved).