In juvenile kyphosis (JK), the roentgenographic defects correspond to the sites of large translucent areas of the collagen-free tissue in the cartilaginous end plates of vertebral bodies. The extent of the roentgenographic lesions is proportional to the number and size of these translucent areas. The gradual transition of radiologic signs between the fully developed JK and the normal spine is paralleled by the decreasing intensity of these histologic change. This relationship can be traced from individual to individual, and within single vertebral columns. The growth zone is often narrow or even missing. The end plates are narrow and segmentally indented towards the vertebral body. These findings are manifestations of the pathogenetic process. Prolapses of disk tissue through gaps in the end plates are probably secondary to the loss of mechanical strength in these defective areas.