Spina bifida occulta is relatively common and is not usually associated with neurological deficit. However, neuroanatomic defects do occur in conjunction with this anomaly. Recently it has been recognized that shortening of the filum terminale of the spinal cord may be associated with spinal bifida occulta. During subsequent growth, traction on the spinal cord causes stretching and deformity of the cord. A family is described in which all 3 siblings manifested the syndrome of tight filum terminale in association with spina bifida occulta of the first sacral segment. Similar vertebral defects were present in both parents. This is believed to be the first reported instance of this condition in which heredity has been considered to be a definite factor.