BACKGROUND: Low-back pain (LBP) is responsible for considerable personal suffering due to pain and reduced function, as well as the societal burden due to costs of health care and lost work productivity. For the vast majority of people with LBP, no specific anatomical cause can be reliably identified. For these people with non-specific LBP there are numerous treatment options, few of which have been shown to be effective in reducing pain and disability. The muscle energy technique (MET) is a treatment technique used predominantly by osteopaths, physiotherapists and chiropractors which involves alternating periods of resisted muscle contractions and assisted stretching. To date it is unclear whether MET is effective in reducing pain and improving function in people with LBP. OBJECTIVES: To examine the effectiveness of MET in the treatment of people with non-specific LBP compared with control interventions, with particular emphasis on subjective pain and disability outcomes. SEARCH METHODS: CENTRAL, MEDLINE, EMBASE, five other databases and two trials registers were searched from inception to May and June 2014 together with reference checking and citation searching of relevant systematic reviews. SELECTION CRITERIA: Randomised controlled trials assessing the effect of MET on pain or disability in patients with non-specific LBP were included. DATA COLLECTION AND ANALYSIS: Two authors independently assessed the risk of bias and extracted the data. Meta-analysis was performed where clinical homogeneity was sufficient. The quality of the evidence for each comparison was assessed with the GRADE approach. MAIN RESULTS: There were 12 randomised controlled trials with 14 comparisons included in the review, with a total sample of 500 participants across all comparisons. Included studies were typically very small (n = 20 to 72), all except one were assessed as being at high risk of bias, and all reported short-term outcomes. For the purposes of pooling, studies were divided into seven clinically homogenous comparisons according to the patient population (acute or chronic LBP) and the nature of the control intervention. Most of the comparisons (five out of seven) included only one study, one comparison had two studies, and one comparison included seven studies.The meta-analyses provided low-quality evidence that MET provided no additional benefit when added to other therapies on the outcomes of chronic pain and disability in the short-term (weighted mean difference (WMD) for pain 0.00, 95% CI -2.97 to 2.98 on a 100-point scale; standardised mean difference (SMD) for disability -0.18, 95% CI -0.43 to 0.08, 7 studies, 232 participants). There was low-quality evidence that MET produced no clinically relevant differences in pain compared to sham MET (mean difference (MD) 14.20, 95% CI -10.14 to 38.54, 1 study, 20 participants). For the comparison of MET to other conservative therapies for acute non-specific LBP, there was very low-quality evidence of no clinically relevant difference for the outcomes of pain (MD -10.72, 95% CI -32.57 to 11.13, 2 studies, 88 participants) and functional status (MD 0.87, 95% CI -6.31 to 8.05, 1 study, 60 participants). For the comparison of MET to other conservative therapies for chronic non-specific LBP, there was low-quality evidence of no clinically relevant difference for the outcomes of pain (MD -9.70, 95% CI -20.20 to 0.80, 1 study, 30 participants) and functional status (MD -4.10, 95% CI -9.53 to 1.33, 1 study, 30 participants). There was low-quality evidence of no clinically relevant difference for the addition of MET to other interventions for acute non-specific LBP for the outcome of pain (MD -3, 95% CI -11.37 to 5.37, 1 study, 40 participants) and low-quality evidence of an effect in favour of MET for functional status (MD -17.6, 95% CI -27.05 to -8.15, 1 study, 40 participants). For chronic non-specific LBP, there was low-quality evidence of an effect in favour of MET for the addition of MET to other interventions for the outcomes of pain (MD -34.1, 95% CI -38.43 to -29.77, 1 study, 30 participants) and functional status (MD -22, 95% CI -27.41 to -16.59, 1 study, 30 participants). Lastly, there was low-quality evidence of no difference for the addition of MET to another manual intervention compared to the same intervention with other conservative therapies for the outcomes of pain (MD 5.20, 95% CI -3.03 to 13.43, 1 study, 20 participants) and functional status (MD 6.0, 95% CI -0.49 to 12.49, 1 study, 20 participants).No study reported on our other primary outcome of general well-being. Seven studies reported that no adverse events were observed, whereas the other five studies did not report any information on adverse events. AUTHORS' CONCLUSIONS: The quality of research related to testing the effectiveness of MET is poor. Studies are generally small and at high risk of bias due to methodological deficiencies. Studies conducted to date generally provide low-quality evidence that MET is not effective for patients with LBP. There is not sufficient evidence to reliably determine whether MET is likely to be effective in practice. Large, methodologically-sound studies are necessary to investigate this question.