Objective: Paramedic fatigue is associated with burnout, attrition, sick leave, work disability, physical and mental health complaints and impaired performance. However, no studies have addressed how fatigue is understood by paramedics. The present study addresses this shortcoming by exploring factors paramedics recognise as contributors to fatigue. Methods: Forty-nine (12F; 38 years ? 9.7 years) Australian paramedics completed a survey on perceived causes of performance impairing fatigue. A total of 107 responses were systematically coded following principles common to qualitative data analysis: data immersion, coding, categorisation and theme generation. Results: Six themes emerged: working time, sleep, workload, health and well-being, work-life balance and environment. Consistent with a scientific understanding of fatigue, prior sleep and wake, time of day and task-related factors were often identified as contributing to fatigue. In other cases, paramedics attributions deviated from a scientific understanding of direct causes of fatigue. Conclusions: These findings demonstrate that paramedics have a broad understanding of fatigue. It is critical to take this into account when discussing fatigue with paramedics, particularly in the case of fatigue education or wellness programmes. These data highlight areas for intervention and education to minimise the experience of paramedic fatigue and the negative health and safety outcomes for paramedics and patients as a result.