400 patients with nonspecific chronic low back pain were included in this study to identify if there was a dose dependent effect of spinal manipulation in this patient population. Patients were randomized to groups receiving 18, 12, 6 or 0 sessions of spinal manipulation from a chiropractor. Session occurred 3 times a week over a 6 week period. At sessions where spinal manipulation was not assigned patients received focused light massage. Results at 52 weeks indicated a modest dose dependent effect, with the 12 session spinal manipulation group demonstrating the most favorable result. However, the difference was not well distinguished from 6 and 18 session interventions, and further research is required to conclusively determine if the number of treatments significantly impacts patient outcomes.