OBJECTIVE : Down syndrome is the most common inherited disorder. Some patients develop atlantoaxial instability. Existing screening guidelines were developed prior to availability of MRI. We present predictors for deficit using dynamic MRI of the craniocervical junction. METHODS : A retrospective review of Down syndrome patients from 2001 to 2015 was carried out. Patients were considered symptomatic if they had clinical deficits or signal change on MRI. Measurements were taken at the atlantoaxial junction and structural abnormalities noted. Analysis was performed with SPSS. RESULTS : A total of 36 patients were included. Patients averaged 93 months of age with a follow-up of 57 months. No asymptomatic patients developed myelopathy during follow-up. During dynamic imaging, symptomatic patients had greater changes in space available for the cord (SAC) (5.2 vs. 2.7 mm; p < 0.001) and atlantodental interval (ADI) (2.8 vs. 1.3 mm; p = 0.04). These patients were also more likely to have a bony anomaly (50 vs. 13%; p = 0.03). CONCLUSIONS : This study characterizes the range of motion seen on dynamic MRI and provides parameters that can be used to distinguish patients at risk for neurologic injury. Changes greater than 3 mm in ADI or 5 mm in SAC during dynamic MRI or any bony abnormality warrants further investigation. Patients without these features may be able to avoid an unnecessary intervention.