Fourteen of 15 myelodysplastic patients evaluated for developmental scoliosis were found to have communicating hydrosyringomyelia, a manifestation of spontaneously arrested hydrocephalus. Eight of these patients had progressive extremity paralysis in addition to the scoliosis. Treatment by ventricular decompression was associated with short term stabilization in 6 early cases of scoliosis. However, more advanced scoliosis in 2 patients continued to progress. Neurologic deficits were improved even in advanced cases by ventricular shunting. The authors propose that hydromyelia and syringomyelia are the cause of developmental scoliosis in myelodysplasia and suggest methods of investigating and treating patients with these conditions.