Case report: We report a 19-year-old girl with a 4-month history of an inability to fully elevate her upper extremity past the horizontal position. Physical examination revealed a winged scapula. MRI was demonstrative of a Chiari I malformation with a small cervical syrinx eccentrically placed to the same side as the dysfunctional extremity. Discussion: We believe this to be the first report of dysfunction of the long thoracic nerve via a hindbrain hernia-induced syrinx with a resultant winged scapula. We would hypothesize that enough anterior horn motor neurons and their axons destined for the long thoracic nerve were injured by the syringomyelia to result in isolated deinnervation of the serratus anterior muscle. Conclusion: The clinician may wish to include syringomyelia in the differential diagnosis of a winged scapula. © Springer-Verlag 2006.