Objective : This study was conducted to examine the correlation between clinical outcomes and the size of the syrinx in post-operative magnetic resonance imaging[MRI] and symptom duration. Methods : The authors investigated twelve patients who underwent various operations for syringomyelia from January 1995 to December 2003. The authors retrospectively analyzed medical records. pre- and post-operative MRI findings, features and durations of symptoms, and the method of surgical treatments. The clinical outcomes were assessed on Prolo scale at 6 months of post-operative period. Results : Neurologic symptoms did not promptly disappear after the shrinkage of syrinx, but post-operative MRI demonstrated most patients showed reductions in the size of the syrinx. There is no statistical relationship between clinical improvements and decrements of the syrinx size. However, patients who underwent surgical treatment within 2 years from the symptom onset had more favorable outcome than those who had operations after 2 years from the onset of symptoms. Conclusion : Change in the size of the syrinx in post-operative MRI is not directly proportional to favorable clinical outcomes. However, symptom duration before surgical treatment has considerable impact on the clinical outcomes.