The three types, Type I (absence of vertebral bodies), Type II (failure of segmentation), and Type III (both), were seen in all sites in the spine, but paraplegia only occurred in unstable Type I lesions (six of twenty-four untreated), some with only moderate kyphosis, and without rapid progression. Without treatment, progression of the kyphos was the rule, averaging 7 degrees per year (thirty patients) and reaching a maximum during the adolescent growth spurt. Brace treatment was ineffective and forty-four patients had surgery. Pseudarthrosis in posterior fusions occurred in half the patients (fifteen of twenty-eight) and in only two of sixteen with combined anteroposterior fusions. Correction with or without Harrington apparatus with posterior fusions before the age of three is the recommended treatment. Where an angulation of over 50 degrees was present, anterior fusion was preferred.