To evaluate pain relief in a lumbar orthosis as a predictor for good clinical results after solid fusion, all patients scheduled for such a surgical procedure were preoperatively encouraged to use an orthosis, soft or rigid, for 3 weeks. Grade of back pain relief as a percent using the orthosis was assessed by the patients and was registered before surgery. After surgery, at 1-year follow-up, patients with nonunion demonstrated radiographically were excluded from the series. Thus, 50 patients with solid fusion could be identified and followed for at least 2 years prospectively. At follow-up these 50 patients graded the pain relief induced by the fusion. In the preoperative corset test, 31 patients experienced significant back pain relief, meaning a reduction of at least 50%. No applicable correlation was found, however, between outcome in this corset test and the eventual clinical result expressed as improvement/no improvement after solid fusion. The two types of orthoses did not differ in this aspect. We conclude that the orthosis, rigid or soft, is not a useful instrument when selecting patients for lumbar fusion.