Quantitative assessments of how trainees affect patient care have been limited, especially in the emergency department (ED). A US study by Pitts et al found that supervised resident visits were associated with greater resource use, including longer length of stay (LOS) in the ED. As EDs host more core clerkship courses, less experienced students have become involved in bedside care. This study examined the association between the presence of medical students in the ED and patient LOS, an established patient-centered outcome and marker of ED performance.