1. The results of 243 thoracoplasty operations are discussed. It was found that scoliosis developed in over 99 per cent of cases and that the curve was convex towards the side of operation. The angle of curvature correlated closely with the number of ribs removed.

2. If the head, neck and tubercle of the rib and the transverse process of the corresponding vertebra were all removed the degree of scoliosis was increased, whereas if a thoracoplasty was performed with apicolysis and embedding of the scapula the spinal deformity was less. Possible explanations for these phenomena are discussed.

3. No evidence was found to support the theory of causation by imbalance between the paired "pneumatic cylinders" (lungs and thoracic cage) supporting the thoracic spine.

4. The scoliosis was found to progress for many years; some factors influencing this course are discussed.

5. No correlation was found between the age of the patient at the time of thoracoplasty and the degree of subsequent scoliosis, but severe spinal deformity can arise even in older adults.