Although health-enhancing weight reductions are associated with behavioural treatments initially, a trajectory towards full regain typically begins within 6-9 months. Women with obesity (body mass index = 30-40 kg m-2 ) who lost at least 3% of their baseline weight within two trials of a new cognitive-behavioural treatment incorporating physical activity prior to changes in eating behaviours, and either regained ≥50% of that weight over 2 years (Regain group, n=32) or continued to lose weight (ContinuedLoss group, n = 34), were assessed from months 6 to 24 on changes in weight-loss behaviours and psychosocial predictors of those behaviours derived from established behavioural theories. For the Regain group, significant decreases in physical activity and fruit/vegetable intake during months 12-24, from both months 6 to 24 and 12 to 24 in eating- and physical activity-related self-regulation and from months 6 to 24 in eating-related self-efficacy (i.e. feelings of ability), were found. No significant behavioural or psychosocial changes were found over those times in the ContinuedLoss group. Changes in self-regulation and self-efficacy completely mediated the relationship between changes in fruit/vegetable intake and group (Regain vs. ContinuedLoss) (McFadden's R 2 = 0.19 and 0.20, respectively), with self-regulation independently contributing to the explained variance. Changes over both months 6-24 and 12-24 in self-regulation significantly mediated the relationship between changes in physical activity and group membership (McFadden's R 2 = 0.24 and 0.27, respectively). Findings suggested that approximately 6 months after treatment initiation would be a suitable time to intervene with some bolstering methods, while approximately 12 months post-initiation would be most applicable for others.