The authors conducted a prospective non-randomised study on the ProDisc intervertebral prosthesis versus anterior lumbar interbody fusion (ALIF). The first group included 14 patients, the second group 10 patients. In the ProDisc group the Oswestry Disability Index improved from +/- 38.42 preoperatively (60 being the worst possible condition) to +/- 15.21 after 6 months and to +/- 12.5 after 12 months. This was definitely better than the ALIF group, where the corresponding figures were +/- 38, +/- 25 and +/- 21.4. The ProDisc patients also scored better with respect to duration of hospitalisation, blood loss and operation time. The complications were comparable in both groups.