345 single-level symptomatic cervical disc disease patients were distributed into either a randomized or non-randomized group. The 209 patients in the randomized group were randomized to receive cervical artificial disc replacement (C-ADR) with ProDisc-C or anterior cervical discectomy and fusion (ACDF), in order to compare the radiographic rates of progressive adjacent level degeneration between the methods. The 136 patients in the non-randomized group were assigned to a continued access (CA) group, in which they underwent C-ADR. Results from 5-7 years exhibited that randomized and non-randomized patients who underwent C-ADR had significantly lower radiographic rates of progressive adjacent level degeneration in comparison to the ACDF group.