BACKGROUND: Some patients suffer from long-lasting symptoms after whiplash injury. However, there are few reports on the long-term changes in the cervical spine after whiplash injury using imaging tests. The purpose of this longitudinal study was to determine the changes on MRI of the cervical spine 20 years after whiplash injury, and to examine the relationships between changes in the cervical spine on MRI and changes in related clinical symptoms. METHODS: Eighty-one subjects finally participated in this study (follow-up rate 16%). The mean follow-up duration was 21.7 years. All subjects filled out a questionnaire about their clinical symptoms. The MRI findings were assessed using numerical grading system applied in the original study. Statistic analyses were used to investigate whether the progression of each MRI finding was associated with the severity of neck pain, stiff shoulders, dizziness and tinnitus. RESULTS: All subjects had complained of some clinical symptoms in the original study: 71 had neck pain, 53 stiff shoulders, and others. In the present study, 66 subjects (81.5%) complained of some clinical symptoms: 57 had stiff shoulders, 20 neck pain, and others. The progression of degeneration on MRI was observed in 95% of the subjects, with C4/5 and 5/6 being the most frequently involved levels. Changes in the severity of neck pain, stiff shoulders, dizziness and tinnitus over 20 years were not significantly associated with the progression of degenerative changes in the cervical spine on MRI. CONCLUSIONS: Twenty years after whiplash injury, 95% of the subjects showed a progression of degeneration in the cervical spine. The progression of the intervertebral disc degeneration in the cervical spine on MRI after whiplash injury was not significantly associated with changes in the severity of related clinical symptoms, indicating that the degenerative changes on MRI may reflect the physiological aging process rather than post-traumatic sequelae.