Context: Acute low back pain (LBP) is a common reason for consultations in primary care. Reducing the pain in the first hours and days and restoring the functional capacity of the lumbar spine may result in a decrease in medical costs and earlier return to work.

Objective: To determine the impact of spinal manipulation on pain and analgesic use in acute low back pain.

Design: Randomised controlled parallel-group trial comparing standard care plus spinal manipulative therapy with standard care alone. Intention-to-treat analysis.

Patients: Outpatients with acute low back pain. Setting: Emergency Department of Bern University Hospital and a primary care practice network.

Inclusion criteria:

1. Age between 20 and 55 years
2. Duration of acute low back pain less than 4 weeks
3. Informed consent

Exclusion criteria:

1. Pregnancy
2. Radicular origin of back pain (with irradiation)
3. Cauda equine syndrome
4. Neurologic deficit
5. Epidural glucocorticoid injections in the preceding three months
6. Previous low back surgery
7. Severe osteoporosis
8. Blood-coagulation disorder
9. Allergy to planned rescue medications
10. Suspicion of a specific cause of low back pain (fracture, tumor, infection, inflammatory disease of the spine, HIV-infection) in the patient's history or by physical examination
11. History or signs of severe dysfunction of the liver or kidney