The overgrowth of cartilaginous and fibrous tissue of the spine in Paget's disease is described in long-term follow-up studies. On cervical manifestation the disease progressed from one vertebrae to the other with destruction of the intervertebral discs, fusion of the vertebral bodies and intervertebral joints and shortening of the affected area. On the lower thoracic and lumbar spine osteomalacia with collapse of the vertebral bodies and biconvex deformities of the discs were seen in the initial period. Several years later the discs flattened, vaulted and fused in the periphery by dystrophic bone. Fusion of the corresponding intervertebral joints and ossification fo the intervertebral ligaments developed. The involved spine was shortened. The sarcroiliacal joint spaces were obliterated in cases with involvement of adjacent bones by Paget's disease. The overgrowth advanced from the periphery towards the center. Ankylosis of sacroiliacal joints has also been observed without fusion of the intervertebral disc spaces. Relatively low age, loss of height, invalidating bone pains and osteomalacia of the pelvis were the main features in cases with spinal changes. Osteomalacia of the spine followed by ossification of intervertebral ligaments and joint capsules and later by vertebral fusion are considered to be a special form of Paget's disease.