Sedentary, overweight women aged 60-70 years were assigned either to a 16-week health education group (/? = 70) in which they were instructed to exercise aerobically on their own three times per week or to a 16-week exercise group (n = 76) that consisted of three supervised aerobic sessions per week. Regression analyses performed at post-test and at 3-, 6-, and 18-months follow-up revealed that exercise frequency was not explained by group membership, but often was negatively associated with placing a greater value on exercising with peers. Those who were exercising more often at 6-and 18-months followup, however, valued the perceived benefits of exercise more highly. A regular exercise program can be beneficial for sedentary older women-especially those who are overweight-because it can reduce their risks for cardiovascular disease, hypertension, diabetes, and musculoskeletal problems (U.S. Dept. of Health and Human Services [USDHHS], 1990[USDHHS], , 1996. Despite the known importance of and preponderance of media attention to exercise, more than 60% of women over age 60 participate in little or no sustained physical activity of at least moderate intensity (Caspersen & Merritt, 1992). When they do initially engage in exercise, adherence often drops dramatically after 6 months (Dishman, 1994;. This has prompted investigators to examine the factors associated with adherence to exercise programs. At the intrapersonal level, some investigations have revealed that those individuals with a greater sense of mastery or self-efficacy and those who are motivated by enjoyment or satisfaction are more likely to maintain regular exercise programs (Avers & Wharton, 1991;Clark, 1996;Lyons & Lachman, 1996;McAuley, Lox, & Duncan, 1993;Oman & McAuley, 1993). Opportunities to socialize and enjoy a sense of camaraderie, for instance, can be primary motivating factors to attend exercise classes (Gillett, 1988). Furthermore, exercise behavior is potentially reinforced when the participant perceives and enjoys its benefits (Emery & Blumenthal, 1990;Emery, Hauck, & Blumenthal, 1992;Gillett, 1988Gillett, , 1993Sharpe et al., 1997).This project was funded by a grant from the National Institute of Nursing Research (R29 NR02087).1 Cerontology Center, University of Utah. Address correspondence to Dr. Michael Caserta, University of Utah Gerontology Center, 10 S 2000 E Front, Salt Lake City, UT 84112-5880. E-mail: mike.caserta@nurs.utah.edu J College of Nursing, University of Utah, Salt Lake City.Older women are often introduced to regular exercise through programs such as community or hospital-based health education classes, where an exercise regimen is prescribed, or through supervised exercise programs, such as aerobic dance or walking clubs (Gillett, White, & Caserta, 1996;Gillett et al., 1993;King, Haskell, Taylor, Kreamer, & DeBusk, 1991). Program features that promote participation include group activities where socialization, support, and a sense of group cohesion and identity are developed, and a sense of comfort is generated from ...