STUDY DESIGN: A systematic review of randomized controlled trials (RCTs). OBJECTIVE: To explore the evidence for the effectiveness of acupuncture for nonspecific low back pain (LBP). SUMMARY OF BACKGROUND DATA: Since the most recent systematic reviews on RCTs on acupuncture for LBP, 6 RCTs have been published, which may impact on the previous conclusions. METHODS: Searches were completed for RCTs on all types of acupuncture for patients with nonspecific LBP published in English. Methodologic quality was scored using the Van Tulder scale. Trials were deemed to be high quality if they scored more than 6/11 on the Van Tulder scale, carried out appropriate statistical analysis, with at least 40 patients per group, and did not exceed 20% and 30% dropouts at short/intermediate and long-term follow-up, respectively. High quality trials were given more weight when conducting the best evidence synthesis. Studies were grouped according to the control interventions, i.e., no treatment, sham intervention, conventional therapy, acupuncture in addition to conventional therapy. Treatment effect size and clinical significance were also determined. The adequacy of acupuncture treatment was judged by comparison of recommendations made in textbooks, surveys, and reviews. RESULTS: Twenty-three trials (n = 6359) were included and classified into 5 types of comparisons, 6 of which were of high quality. There is moderate evidence that acupuncture is more effective than no treatment, and strong evidence of no significant difference between acupuncture and sham acupuncture, for short-term pain relief. There is strong evidence that acupuncture can be a useful supplement to other forms of conventional therapy for nonspecific LBP, but the effectiveness of acupuncture compared with other forms of conventional therapies still requires further investigation. CONCLUSION: Acupuncture versus no treatment, and as an adjunct to conventional care, should be advocated in the European Guidelines for the treatment of chronic LBP.