Study Design. A randomized clinical trial. Objectives. To assess the efficacy of motorized continuous traction for low back pain. Summary of Background Data. The available studies on the efficacy of lumbar traction do not allow clear conclusions because of severe methodologic flaws. The current trial aimed to overcome these shortcomings. Methods. Patients with at least 6 weeks of nonspecific low back pain were selected. High-dose traction was compared with sham (or low-dose) traction. Sham traction was given with a specially developed brace that becomes tighter in the back during traction. This was experienced as if real traction were exerted. The patients and the outcome assessor were unaware of treatment allocation. Outcome measures were patient's global perceived effect, severity of main complaints functional status, pain, range of motion, work absence, and medical treatment. Results for the outcome measures at 12 weeks and 6 months after randomization are presented. Results. One hundred and fifty-one patients were randomly allocated to one of the two treatment methods. Intention-to-treat analysis of the 12-week and 6-month results showed no statistically significant differences between the groups on all outcome measures; all 95% confidence intervals included the value zero. The number of patients lost to follow-up study was, very low. Other analyses showed the same results. Conclusions. Most common flaws of earlier studies on traction therapy could be overcome. This trial did not support the claim that traction is efficacious for patients with low back pain.