In order to explore the concept that scoliosis is fundamentally a loss of 
left-right symmetry. surface topography was used to measure asymmetry in three 
dimensions at three levels on the back surface. Statistical analysis of 
prospectively collected topographic, radiographic and clinical data, in girls 
with adolescent idiopathic scoliosis, was carried out and comparisons were made 
with theoretically perfect symmetry (test value of zero). All scoliosis showed 
statistically significant differences in coronal dimensions, index points on the 
convex side of the scoliosis being further from the mid-line than those on the 
concave side. Primary thoracic scoliosis differed from thoracolumbar and lumbar 
in that they showed directional asymmetry at all levels and in all directions, 
the side of the scoliosis convexity being broader, taller and thicker. This 
asymmetry is not due to posture, spinal balance or trunk rotation, as left and 
right sides are being compared independently of their orientation in space. The 
asymmetry is of size in three dimensions and size is determined by growth. 
Growth is a three dimensional process, but does not necessarily occur equally in 
all three. Differential growth is both directional and regional, particularly 
during the pubertal growth spurt, when proportions change substantially, and is 
controlled by many genes, as well as by hormones and signalling molecules. The 
implication is that scoliotic deformity is the result of asymmetric growth, not 
confined to the vertebrae, but affecting the entire trunk. This is a 
developmental, rather than pathological, phenomenon. It makes questions of 
aetiology redundant and natural history logical.