BackgroundOveruse of lumbar imaging in the Emergency Department is a well-recognised healthcare challenge. Studies to date have not provided robust evidence that available interventions can reduce overuse. For an intervention aimed at reducing imaging to be effective, insight into how both patients and clinicians view lumbar imaging tests is essential.AimTo explore factors that might influence overuse of lumbar imaging in the Emergency Department.MethodsParticipants were recruited from three hospitals in Sydney, Australia between April and August 2019. We conducted focus groups and/or interviews with 14 patients and 12 clinicians. Sessions were audio-recorded and transcribed verbatim. Data were analysed using framework analysis by a team of four researchers with diverse backgrounds.ResultsPatients described feeling that the decision about lumbar imaging was made by their Emergency Department clinician and reported little involvement in the decision-making process. Other potential drivers of lumbar imaging overuse from the patients’ perspective were strong expectations for lumbar imaging, a reluctance to delay receiving a diagnosis, and requirements from third parties (eg, insurance companies) to have imaging. Emergency Department clinicians suggested that the absence of an ongoing therapeutic relationship, and the inability to manage perceived patient pressure could drive overuse of lumbar imaging. Suggested protective factors included: involving patients in the decision, ensuring clinicians have the ability to explain the reasons to avoid imaging and collaborative approaches to care both within the Emergency Department and with primary care.Conclusion and key findingsWe found several factors that could contribute to overuse of lumbar imaging in the Emergency Department. Solutions to overuse of lumbar imaging in the Emergency Department could include: (1) strategies to involve patients in decisions about imaging; (2) training and support to provide thorough and well explained clinical assessment for low back pain; and (3) systems that support collaborative approaches to care.