Atlanto-occipital subluxation (AOS) in individuals with Down syndrome is discussed using five new cases and nine patients previously presented in the literature. Although AOS is likely due to ligamentous laxity, it was associated with atlantoaxial instability in only two youngsters. Reducible C1-C2 rotary subluxation was present in a third. Posterior movement of the occiput with respect to C1 occurred on extension and reduced on flexion in all but one individual who demonstrated anterior subluxation. Neurological problems are described in only two individuals: one with severe atlantoaxial subluxation (AAS) and the other with multiple cervical spine anomalies. Since AOS is usually detected on films obtained to screen children with Down syndrome for AAS, the atlanto-occipital joint should be carefully studied on these radiographs. The clinical significance of AOS needs to be determined.