We sought to determine how often Emergency Physicians (EPs) order plain radiographs (XRs) of the lumbosacral spine in evaluating patients with low back pain (LBP). In addition, we sought to determine what history and physical examination findings were statistically associated with the use of an XR. Patients evaluated in our Emergency Department (ED) between April 1, 1995 and September 30, 1995 for LBP were identified retrospectively by their ICD-9 discharge code. The ED record was reviewed, and an odds ratio (OR) was calculated for each of several history and physical examination findings, to determine which of them increased the likelihood of having an XR. Forty of 214 patients (19%) with LBP had an XR done. Patient characteristics associated with the use of an XR were: a positive straight leg examination, age > 50 years, a history of trauma, and vertebral tenderness. In this series, only a small minority of patients with LBP had an XR done as part of their ED evaluation. The choice of which patients to image was determined by history and physical examination findings. We conclude that the EPs we studied are evaluating LBP as conservatively, if not more so, than physicians in other specialties.