Although family caregivers of patients with lung and other cancers show high rates of psychological distress, they underuse mental health services. This qualitative study aimed to identify barriers to mental health service use among 21 distressed family caregivers of lung cancer patients. Caregivers had not received mental health services during the patient's initial months of care at a comprehensive cancer centre in New York City. Thematic analysis of interview data was framed by Andersen's model of health service use and Corrigan's stigma theory. Results of our analysis expand Andersen's model by providing a description of need variables (e.g. psychiatric symptoms), enabling factors (e.g. finances), and psychosocial factors associated with caregivers' non-use of mental health services. Regarding psychosocial factors, caregivers expressed negative perceptions of mental health professionals and a desire for independent management of emotional concerns. Additionally, caregivers perceived a conflict between mental health service use and the caregiving role (e.g. prioritising the patient's needs). Although caregivers denied stigma associated with service use, their anticipated negative self-perceptions if they were to use services suggest that stigma may have influenced their decision to not seek services. Findings suggest that interventions to improve caregivers' uptake of mental health services should address perceived barriers.