Context: Advanced lung cancer patients typically have a poor prognosis and many symptoms that interfere with functioning, contributing to high rates of emotional distress in both patients and family caregivers. There remains a need for evidence-based interventions to improve functional outcomes and distress in this population.; Objectives: This pilot trial examined the feasibility and preliminary efficacy of telephone-based Acceptance and Commitment Therapy (ACT) for symptomatic, advanced lung cancer patients and their distressed family caregivers. Primary outcomes were patient symptom interference with functioning and patient and caregiver distress.; Methods: Symptomatic, advanced lung cancer patients and distressed caregivers (n=50 dyads) were randomly assigned to six sessions of ACT or an education/support condition. Patients completed measures of symptom interference and measures assessing the severity of fatigue, pain, sleep disturbance, and breathlessness. Patients and caregivers completed measures of distress and illness acceptance and struggle.; Results: The eligibility screening rate (51%) and retention rate (76% at 6 weeks post-intervention) demonstrated feasibility. No group differences were found with respect to patient and caregiver outcomes. Both groups showed a small, significant decrease in struggle with the illness over the study period, but did not show meaningful change in other outcomes.; Conclusion: Findings suggest that telephone-based ACT is feasible for many advanced lung cancer patients and caregivers, but may not substantially reduce symptom interference and distress. Low baseline levels of certain symptoms may have contributed to null findings. Next steps include applying ACT to specific, clinically meaningful symptom interference and varying intervention dose and modality.