Atlantoaxial instability is a relatively frequent finding in Down syndrome, but syringomyelia is a rare symptom. A four-year-old girl with Down syndrome was noted to have one year history of torticollis and progressive motor deterioration presenting with abnormal gait, ataxia or quadriparesis for the past three months. She was admitted because of acute urinary retention. Physical examination showed distended urinary bladder, hyperreflexia, bilateral ankle clonus and the existence of Babinski's signs. The x-ray films of the cervical spine showed widening between the joint space of atlas and odontoid processes. Magnetic resonance imaging revealed C1-C2 subluxation with syringomyelia. After bladder training and cervical orthosis, the symptoms improved.