This article was updated on November 12, 2019, because of a previous error. On page 349, in Table VII, the column heads “2 Yr”, “Mean Change from Baseline (SE)”, “Difference in Mean Change (95% CI)”, and “P Value” that had been aligned with the content in the second to fourth columns have now been aligned with the content in the third to fifth columns.An erratum has been publishedJ Bone Joint Surg Am. 2019 Dec 18;101(24):e138. BACKGROUND:The effectiveness of operative compared with nonoperative treatment at initial presentation (no prior fusion) for adult lumbar scoliosis has not, to our knowledge, been evaluated in controlled trials. The goals of this study were to evaluate the effects of operative and nonoperative treatment and to assess the benefits of these treatments to help treating physicians determine whether patients are better managed operatively or nonoperatively. METHODS:Patients with adult symptomatic lumbar scoliosis (aged 40 to 80 years, with a coronal Cobb angle measurement of ≥30° and an Oswestry Disability Index ODI score of ≥20 or Scoliosis Research Society SRS-22 score of ≤4.0) from 9 North American centers were enrolled in concurrent randomized or observational cohorts to evaluate operative versus nonoperative treatment. The primary outcomes were differences in the mean change from baseline in the SRS-22 subscore and ODI at 2-year follow-up. For the randomized cohort, the initial sample-size calculation estimated that 41 patients per group (82 total) would provide 80% power with alpha equal to 0.05, anticipating 10% loss to follow-up and 20% nonadherence in the nonoperative arm. However, an interim sample-size calculation estimated that 18 patients per group would be sufficient. RESULTS:Sixty-three patients were enrolled in the randomized cohort30 in the operative group and 33 in the nonoperative group. Two hundred and twenty-three patients were enrolled in the observational cohort112 in the operative group and 111 in the nonoperative group. The intention-to-treat analysis of the randomized cohort found that, at 2 years of follow-up, outcomes did not differ between the groups. Nonadherence was high in the randomized cohort (64% nonoperative-to-operative crossover). In the as-treated analysis of the randomized cohort, operative treatment was associated with greater improvement at the 2-year follow-up in the SRS-22 subscore (adjusted mean difference, 0.7 95% confidence interval (CI), 0.5 to 1.0) and in the ODI (adjusted mean difference, −16 95% CI, −22 to −10) (p < 0.001 for both). Surgery was also superior to nonoperative care in the observational cohort at 2 years after treatment on the basis of SRS-22 subscore and ODI outcomes (p < 0.001). In an overall responder analysis, more operative patients achieved improvement meeting or exceeding the minimal clinically important difference (MCID) in the SRS-22 subscore (85.7% versus 38.7%; p < 0.001) and the ODI (77.4% versus 38.3%; p < 0.001). Thirty-four revision surgeries were performed in 24 (14%) of the operative patients. CONCLUSIONS:On the basis of as-treated and MCID analyses, if a patient with adult symptomatic lumbar scoliosis is satisfied with current spine-related health, nonoperative treatment is advised, with the understanding that improvement is unlikely. If a patient is not satisfied with current spine health and expects improvement, surgery is preferred. LEVEL OF EVIDENCE:Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.