One hundred and eighty six patients with high severity nonspecific chronic low back pain (LBP) were randomized to receive either osteopathic manual treatment (OMT) or a sham-controlled OMT treatment. The purpose of this study was to investigate the short-term effectiveness of OMT in terms of initial clinical response, subsequent stability of response and the final response of the patients. Clinical response was assessed at weeks 1, 2, 4, 6, 8 and 12 where >50% improvement on a 100-mm Visual Analogue Scale (VAS) score indicated substantial alleviation in LBP. Results demonstrated that patients treated with OMT displayed more stable clinical responses which occurred earlier than the control group, without subsequent relapse at the end of the 12 week period.