Abnormality of CSF hydrodynamics is an important factor of the pathogenesis of syringomyelia. Recent development of cine-MRI visualized real time CSF movement in the syrinx or subarachnoid space. In the present study, twenty cases of syringomyelia associated with Chiari I malformation, 10 cases of syringomyelia associated with spina bifida aperta, and 10 cases of syringomyelia associated with spina bifida occulta were studied with MRI and cine-MRI. The result demonstrated that hydrodynamics of these three groups were different to each other. Chiari I malformation showed CSF hydrodynamic abnormality at the foramen magnum and marked flow void in the syrinx. On the other hand, myelomeningocele showed hydrocephalus and less prominent flow void in the syrinx. Spinal lipoma which is the majority of spina bifida occulta showed no abnormality of CSF hydrodynamics. In conclusion, the selection of treatments should be individualized depending on the hydrodynamical abnormality of each patient.