BACKROUND AND PURPOSE: Our purpose was to investigate the association between cervicomedullary neuroschisis and mirror movements in patients with Klippel-Feil syndrome (KFS). METHODS: We conducted a retrospective analysis of 23 patients with KFS who were seen at our institution during a 10-year period. Sixteen of the 23 patients had undergone adequate axial view cross-sectional imaging of the upper cervical spine. The degree of neuroschisis was assessed for each patient, using an objective scoring system. Twelve patients were evaluated for the presence or absence of mirror movements. RESULTS: A high percentage of female patients with KFS was noted (17 [74%] of 23 patients). Adequate cross-sectional images were available for 16 of the 23 patients, six (38%) of whom had some form of cervicomedullary neuroschisis. Five of the six patients had been clinically evaluated, and all were shown to have mirror movements. One patient with Chiari II malformation, which obscured evaluation for neuroschisis, also had mirror movements. Of the remaining nine patients without cervicomedullary neuroschisis, six were evaluated, and none of the six had mirror movements. A review of the theoretical neuroanatomic basis of mirror movements is presented herein, and neurosurgical management concerns for patients with KFS are discussed. CONCLUSION: A strong association exists between cervicomedullary neuroschisis and mirror movements in cases of KFS. Screening of patients with mirror movements may help identify clinically unsuspected KFS and may also help stratify risk within this patient population, identifying patients who might benefit from early neurosurgical intervention.