A 7-year-old boy with Apert's syndrome and hydrocephalus presented with scoliosis and lower extremity weakness. Neuroradiological evaluation demonstrated bony abnormalities involving the foramen magnum and a markedly hydromyelic spinal cord. Clinical improvement followed posterior fossa decompression and a myelotomy on the caudal conus medullaris. A possible role of the craniofacial anomaly in the pathogenesis of the hydromyelia is discussed.