In a large study of the use of acupuncture for the treatment of around 10,000 patients with chronic low back pain, acupuncture was found to be more effective than a no-acupuncture control group and relatively cost-effective.

Pragmatic randomized trial evaluating the clinical and economic effectiveness of acupuncture for chronic low back pain. Am J Epidemiol. 2006 Sep 1;164(5):487-96

and

A meta-analysis of 33 randomised controlled trials of acupuncture has concluded that it can effectively relieve chronic lower back pain. Specifically it was found to be more effective than sham acupuncture and no additional treatment. 

Annals of Internal Medicine, Vol. 142, Issue 8, pages 651-663