Although not recommended for low back pain, the efficacy of systemic corticosteroids has never been evaluated in a general low back pain population. To test the efficacy of systemic corticosteroids for Emergency Department (ED) patients with low back pain, a randomized, double-blind, placebo-controlled trial of long-acting methylprednisolone was conducted with follow-up assessment 1 month after ED discharge. Patients with non-traumatic low back pain were included if their straight leg raise test was negative. The primary outcome was a comparison of the change in a numerical rating scale (NRS) 1 month after discharge. Of 87 subjects randomized, 86 were successfully followed to the 1-month endpoint. The change in NRS between discharge and 1 month differed between the two groups by 0.6 (95% confidence interval -1.0 to 2.2), a clinically and statistically insignificant difference. Disability, medication use, and healthcare resources utilized were comparable in both groups. Corticosteroids do not seem to benefit patients with acute non-radicular low back pain.