We identified factors associated with radiograph evaluation for patients who presented to the Emergency Department (ED) with uncomplicated low back pain (LBP). Using 1998-2000 ED data from the National Hospital Ambulatory Medical Care Survey, a multivariate analysis was performed to assess utilization of radiographs for LBP. Based upon published guidelines, of the over 3 million patients who met our criteria of uncomplicated LBP, 17.8% received an unnecessary radiograph. Patients who arrive via ambulance with moderate pain, who need to be seen within 15 min, and who have 3 or more screening tests ordered are 100% likely to also get a radiograph. There is an increased probability of receiving a radiograph for those patients 40-70 years old, being seen at a metropolitan hospital, having private insurance, and being treated by a resident in training. Multiple factors are associated with the overuse of radiographs for patients presenting with uncomplicated LBP.