Structural Integration (SI) is an alternative method of manipulation and movement education. To obtain preliminary data on feasibility, effectiveness, and adverse events (AE), 46 outpatients from Boston area with chronic nonspecific low back pain (CNSLBP) were randomized to parallel treatment groups of SI plus outpatient rehabilitation (OR) versus OR alone. Feasibility data were acceptable except for low compliance with OR and lengthy recruitment time. Intent-to-treat data on effectiveness were analyzed by Wilcoxon rank sum, n = 23 per group. Median reductions in VAS Pain, the primary outcome, of -26 mm in SI + OR versus 0 in OR alone were not significantly different (P = 0.075). Median reductions in RMDQ, the secondary outcome, of -2 points in SI + OR versus 0 in OR alone were significantly different (P = 0.007). Neither the proportions of participants with nor the seriousness of AE were significantly different. SI as an adjunct to OR for CNSLBP is not likely to provide additional reductions in pain but is likely to augment short term improvements in disability with a low additional burden of AE. A more definitive trial is feasible, but OR compliance and recruitment might be challenging. This trial is registered with ClinicalTrials.gov (NCT01322399).