The aim of this work was to add to the body of data on the frequency and severity of degenerative radiographic findings at adjacent levels after anterior cervical interbody fusion and on their clinical impact and to contribute to the insights about their pathogenesis. One hundred eighty patients who were treated by anterior cervical interbody fusion and who had a follow-up of >60 months were clinically and radiologically examined by independent investigators. For all patients, the long-term Odom score was compared with the score as obtained 6 weeks after surgery. For myelopathic cases, both the late Nurick and the Odom score were compared with the initial postoperative situation. For the adjacent disc levels, a radiologic “degeneration score” was defined and assessed both initially and at long-term follow-up. At late follow-up after anterior cervical interbody fusion, additional radiologic degeneration at the adjacent disc levels was found in 92% of the cases, often reflecting a clinical deterioration. The severity of this additional degeneration correlated with the time interval since surgery. The similarity of progression to degeneration between younger trauma patients and older nontrauma patients suggests that both the biomechanical impact of the interbody fusion and the natural progression of pre-existing degenerative disease act as triggering factors for adjacent level degeneration.