The purpose of this study was to determine the value of flexion and extension MR in traumatized cervical spines following rear low-impact acceleration-deceleration injury. The cervical spines of 100 consecutive uninjured normal asymptomatic adults and 100 adult accident victims following rear low-impact motor vehicle accidents were evaluated using rapid T2-weighted MRI. Subjects were matched for age but not gender. The age range was 18 to 53 years, with a mean of 35 years. Injured subjects were evaluated during the subacute period, at 12 to 14 weeks after injury, following clinically resolved muscle spasm. Imaging findings were compared between normal and injured subjects. The normal subjects showed a stepwise segmental motion pattern that started at C1-C2 and transmitted to the lower cervical segments. Loss of normal cervical lordosis (hypolordosis) was observed in 4% (4 of 100) patients. Normal range of motion (rounded to the nearest 5 masculine ) was quantified as 50 masculine flexion (range, 45-65 masculine; standard deviation, 6.5 masculine ) and 60 masculine extension (range, 50-70 masculine; standard deviation, 6.5 masculine ). Asymptomatic disk herniations were observed in 2% (2 of 100) patients. In the subacute post-traumatic subjects, there was a loss of the normal segmental motion pattern, with hypolordosis in 98% (98 of 100) patients. Range of motion (rounded to the nearest 5 masculine ) was restricted, quantified as 25 masculine flexion (range, 5-40 masculine; standard deviation, 15 masculine ) and 35 masculine extension (range, 20-50 masculine; standard deviation, 10 masculine ). Disk herniations were observed in 28% (28 of 100) patients. Biomechanical changes in the herniated disk were noted, with mildly increased spinal stenosis following flexion. The authors conclude that flexion and extension MR can be a valuable adjunct examination in the evaluation of patients in the clinical setting of subacute cervical spine trauma.