Objective: To critically and systematically review methods used to estimate the smallest worthwhile effect of interventions for nonspecific low back pain. Study Design and Setting: A computerized search was conducted of MEDLINE, CINAHL, LILACS, and EMBASE up to May 2011. Studies were included if they were primary reports intended to measure the smallest worthwhile effect of a health intervention (although they did not need to use this terminology) for nonspecific low back pain. Results: The search located 31 studies, which provided a total of 129 estimates of the smallest worthwhile effect. The estimates were given a variety of names, including the Minimum Clinically Important Difference, Minimum Important Difference, Minimum Worthwhile Reductions, and Minimum Important Change. Most estimates were obtained using anchor- or distribution-based methods. These methods are not (or not directly) based on patients' perceptions, are not intervention-specific, and are not formulated in terms of differences in outcomes with and without intervention. Conclusion: The methods used to estimate the smallest worthwhile effect of interventions for low back pain have important limitations. We recommend that the benefit-harm trade-off method be used to estimate the smallest worthwhile effects of intervention because it overcomes these limitations. © 2012 Elsevier Inc. All rights reserved.