The Dynesys fixation device has fewer side effects and complications than conventional fusion techniques, but indications for its use are still unclear. This prospective study of 50 patients treated since October 2000 aimed to determine its efficacy and to establish contra-indications. Patients considered for lumbar spinal fusions were evaluated to assess whether Dynesys fixation could be used instead of conventional fusion techniques. All patients completed an Oswestry questionnaire preoperatively and again three and six months postoperatively. Postoperatively all patients were mobilised on day one or two, using only a soft back brace. No limitations were placed on sitting or driving. All Oswestry and visual pain analogue scores improved dramatically in the short term. Complications included loosening of screws that made further surgery necessary. Three patients required conversion to fusion and one developed disc reherniation. In the right patient, this method is very effective. All the older patients were clearly better off with this technique, which permits early mobilisation and return to work. The swiftness with which the procedure can be carried out means less exposure, less bleeding and ultimately less fibrosis. Absolute contra-indications are spinal instability (including spondylolisthesis), deformity (including severe degenerative scoliosis), long fixations and revision discectomy. Relative contra-indications include uncomplicated mini-discectomy where no fixation is required and use in very active younger patients