Clinical response and relapse following a regimen of osteopathic manual treatment (OMT) were assessed in patients with chronic low back pain (LBP) within the OSTEOPATHIC Trial, a randomized, double-blind, sham-controlled study. Initial clinical response and subsequent stability of response, including final response and relapse status at week 12, were determined in 186 patients with high baseline pain severity (≥50 mm on a 100-mm visual analogue scale). Substantial improvement in LBP, defined as 50% or greater pain reduction relative to baseline, was used to assess clinical response at weeks 1, 2, 4, 6, 8, and 12. Sixty-two (65%) patients in the OMT group attained an initial clinical response vs. 41 (45%) patients in the sham OMT group (risk ratio [RR], 1.45; 95% confidence interval [CI], 1.11-1.90). The median time to initial clinical response to OMT in these patients was 4 weeks. Among patients with an initial clinical response prior to week 12, 13 (24%) patients in the OMT group vs. 18 (51%) patients in the sham OMT group relapsed (RR, 0.47; 95% CI, 0.26-0.83). Overall, 49 (52%) patients in the OMT group attained or maintained a clinical response at week 12 vs. 23 (25%) patients in the sham OMT group (RR, 2.04; 95% CI, 1.36-3.05). The large effect size for short-term efficacy of OMT was driven by stable responders who did not relapse.