The use of spinal orthoses for chronic low back pain has traditionally been random and empirical. Frequently, a lumbosacral corset is prescribed and, upon failure of the corset to reduce pain, orthotic treatment is abandoned. In this prospective study, the test instrument of Willner, consisting of a rigid aluminum thoracic lumbosacral orthosis (TLSO) with a sagittal lumbar pad that is adjustable in lumbar flexion or extension, is used to test the hypothesis that a five-day trial in a test orthosis will be a good predictor of the outcome of orthotic treatment for chronic low back pain.