With increasing evidence supporting physical activity benefits during breast cancer treatment, addressing exercise adherence with consideration of the unique exercise barriers, outcome expectations and preferences of cancer patients is needed. Our pilot study aimed to determine the following during breast cancer treatment: (1) exercise barriers, outcome expectations/values and associations with exercise stage of change and (2) exercise preferences. A cross-sectional survey was administered to 23 breast cancer patients during treatment. Participants were primarily aged 50-60 years (52%), Caucasian (91%), with stage I (30%), II (44%) or III (26%) disease. A total of 48% were receiving chemotherapy. In total, 50% were in the pre-contemplation/contemplation stage of change, with 34% in action/maintenance. Common exercise adherence barriers (i.e. lack of priority, self-discipline, procrastination and fatigue) demonstrated statistically significant negative associations with exercise. Frequent outcome expectations included improving heart/lungs, reducing disease risk, building muscle strength and losing weight. Important outcomes included improving state of mind, reducing fatigue and avoiding injury. Outcome expectations (i.e. less depression, boredom and nausea) were positively associated with exercise. The majority preferred walking (100%), moderate-intensity (61%), home-based (78%) exercise. Among breast cancer patients during treatment, exercise adherence barriers are general and disease specific. Outcome expectations are physical benefits, with the most important outcomes being psychological or avoidance of risk (i.e. injury). © 2006 Blackwell Publishing Ltd.