Background The benefts of exercise, even at low intensity levels, in improving overall health, psychological well-being, and quality of life in patients with cancer have been well documented. However, few patients are involved in formal exercise programs, and little is known about the factors that motivate those who do participate. Although it has not been well assessed, it stands to reason that spousal and family support is an important determinant of cancer patients' adoption of, and adherence to, an exercise program. Objective To characterize attitudes among the family caregivers of patients with late-stage lung cancer about their role in promoting exercise. Methods 20 adult family caregivers of patients with stage IIIB or IV non-small-cell lung cancer were asked during semistructured interviews about their views on the role of exercise in "fghting cancer," whether with respect to survival, health, psychological well-being, or overall quality of life; their ability to encourage patients to exercise; and their receptivity to getting exercise instructions from health care providers. Findings Family caregivers viewed exercise as important in fghting cancer. Past exercise patterns and lifestyle were important considerations, with some family caregivers who had not previously exercised considering household activities suffcient for promoting ftness. Family caregivers emphasized the importance of knowing the established boundaries of their relationships and respecting patients' autonomy. Caregivers generally thought that direction from health care providers to exercise would more likely result in meaningful behavioral change for patients. Limitations The participants were recruited from a quaternary medical center and restricted to those with lung cancer, which may limit the generalizability of the fndings to other settings or cancers. Conclusions and interpretation Family caregivers believe that exercise is important for patients, but feel constrained in their willingness and ability to promote exercise behaviors because of the established boundaries of their relationships. They have mixed opinions about the utility of exercise promotion by health care providers. Family caregivers are ambivalent about promoting exercise for patients with advanced cancer. Nonjudgmental assessment of patients' past exercise preferences and established relationship boundaries should inform clinical judgment about the utility of engaging family caregivers in the promotion of exercise.