BACKGROUND: Despite the many known benefits of physical activity, some women (27%) report no leisure-time physical activity in the prior month. Of those women who began an exercise program, the dropout rate was as high as 50% in the first 3-6 months. The challenge for researchers and clinicians is to identify those factors that influence not only adoption, but also maintenance, of physical activity. OBJECTIVE: The purpose of this study was (a) to describe midlife women's maintenance of walking following the intervention phase of a 24-week, home-based walking program, and (b) to identify the effects of background characteristics, self-efficacy for overcoming barriers to exercise, and adherence to walking during the intervention phase on retention and adherence to walking. METHODS: There were Black and White women participants (N = 90) aged 40-65 years who completed a 24-week, home-based walking program. Self-efficacy for overcoming barriers to exercise, maximal aerobic fitness, and percentage of body fat were measured at baseline, 24 weeks, and 48 weeks. Adherence was measured with heart-rate monitors and an exercise log. RESULTS: Retention was 80% during maintenance. On average, the women who reported walking during maintenance adhered to 64% of the expected walks during that phase. Examination of the total number of walks and the number and sequence of weeks without a walk revealed dynamic patterns. The multiple regression model explained 40% of the variance in adherence during the maintenance phase. DISCUSSION: These results suggest that both self-efficacy for overcoming barriers and adherence during the intervention phase play a role in women's walking adherence. The findings reflect dynamic patterns of adopting and maintaining new behavior.