A review of the literature suggests that implanting current artificial discs for degenerative disc disease at one level of the lumbar spine is as safe and effective as fusion, but is not a substantially better procedure. There are no controlled trials of multilevel implantation, and the literature suggests that this should, therefore, be considered experimental surgery. There is evidence that adjacent levels are not protected from degeneration, and degeneration of the zygapophysial joints at the operated level may occur. The concept of motion preservation is unproven and needs to be reviewed.