General practitioners (GPs) use of imaging for acute low back pain (LBP) is above guideline recommendations, and the reasons for this remain under-researched. We examined the perspectives, expectations and information needs of Australian GPs requesting lumbar spine diagnostic imaging for patients presenting with acute LBP.We completed semi-structured interviews with 12 GPs practising in Victoria, Australia. Transcripts were thematically analysed, and themes compared according to whether or not GPs reported they regularly requested imaging for LBP.We identified four themes. (1) Besides responding to 'red flags', GPs' experiences of uncovering unexpected but serious findings on imaging for LBP as well as perceived external pressures motivated their defensive imaging practices. (2) While most were reluctant to request imaging for LBP, once requested, GPs escalated through imaging modalities and focused on the diagnostic benefit of their findings. (3) GPs supported the inclusion of epidemiological data on imaging reports, but (4) largely opposed imaging reports being written in plain language, believing reports to be clinician-to-clinician communications that patients would misunderstand. All GPs were aware of the limited utility of imaging for diagnosing LBP, and themes were similar between GPs who regularly requested imaging and those who did not. Factors other than knowledge of imaging efficacy for LBP seemed to play an important role in imaging requests.Our study identified key drivers of imaging use for LBP in primary care. The findings underscore that interventions targeting GPs addressing the overuse of imaging for LBP should transcend knowledge deficit models.