Fluid cavities extending beyond several segments within the spinal cord comprise a pathologic entity that is not a disease, but a condition with many possible causes. Hindbrain herniation with or without associated arachnoid thickening is the most common cause, followed by spinal arachnoiditis, especially with paraplegia and also intraspinal tumors. The presentation may be variable, particularly in the hindbrain-related cases, and the final clinical picture is convergent because the pattern of destruction of the cord is determined by planes of weaknesses. It is almost always a surgical condition. The destructive forces are those of fluid cutting into the tissues, and expeditious and careful surgery is often successful, particularly if practiced early. The surgery should be planned to deal with raised CSF pressure and hydrocephalus, then the likely filling mechanism. Suck, the development of pressure differences acting over several seconds and deforming parts of the neuraxis such as a HBH, may provide a filling mechanism. Slosh, the impulsive rapid movement of CSF within the syrinx, both upward and downward, provides a continuing destructive force and may also be partly responsible for filling. Drainage of the syrinx may be a useful supplementary procedure and is conveniently combined with operation on the nonhindbrain-related cases. Drainage in these cases should not usually be at the widest part of the syrinx, tempting though that may be, but should be combined, where possible, with an attempt to correct the filling mechanism present at the site of the pathology. The ideas in this article are simple, but the surgical management of the various problems is not easy. The syringomyelic cord is fragile, neurologic losses are likely to be permanent, as are orthopedic problems such as Charcot's joints and kyphoscoliosis. Future management problems will include cases in which HBH or syringomyelia comes to light as an unexpected finding on MRI. If neurologic deficits are allowed to develop, they are likely to be irreversible and permanently affect the patients.