Purpose The aim of this study is to explore breast cancer survivors' experience of a weight loss intervention and identify potential facilitators and barriers of initiating and maintaining weight, dietary or physical activity changes. Method Fourteen women randomised to and completing the 12-month weight loss intervention completed semi-structured interviews 7.5 +/- 0.5 months after intervention completion. An inductive thematic analysis was conducted whereby interviews were independently coded and themes identified. Results Women were (mean +/- SD) 55.6 +/- 8.5 years, 30.2 +/- 4.6 kg/m(2) and 17.1 +/- 3.4 months post-diagnosis at study baseline. Four themes emerged: (1) perceived motivation to participate in the intervention, (2) facilitators, (3) challenges and (4) maintenance of weight loss and behaviour changes. All women noted the impact of social/family environments, either to facilitate (e.g., support from family members) or impede (e.g., major family event) changes. The structure and support of the intervention, particularly accountability to their coach, was also seen as facilitating. Formation of habitual physical activity facilitated dietary changes. Dietary change strategies most perceived to facilitate weight loss were reducing energy intake by dietary self-monitoring, increasing vegetable intake and portion control. Challenges included breast cancer-specific issues such as post-diagnosis weight gain, treatment-related side effects and psychological issues around readiness to change and self-regulation. Diminished accountability following intervention completion impacted the maintenance of weight loss and behaviour changes, notably dietary self-monitoring. Conclusions Results suggest that formal involvement of a support person (e.g. family member/friend) and referring women to ongoing, community-based services to maintain patient-perceived accountability may be particularly useful strategies for future weight loss intervention trials targeting women with breast cancer.