The authors observed 10 blocks of from 2 to 8 vertebrae in 7 patients whose spines were affected by Paget's disease. The morphological characteristics of these blockages were for the most part similar to those of acquired synostoses, the corresponding articular apophyses appearing to be fused in the majority of cases. Even without a radiograph taken before the formation of the blocks, the fact that there had been progression of the synostosis between certain vertebrae indicates the probability of an acquired origin. The prevalence of these vertebral blocks in a group of 76 patients suffering from Paget's disease of the spine (12 percent, or 9 patients with 13 blocks) was significantly higher than that found in a population of 200 persons not suffering from Paget's disease, (3 percent, or 6 patients with 6 blocks) and among the 13 blocks discovered in the patients with Paget's disease only 3 were formed of vertebrae unaffected by deforming osteitis. These facts suggest that the formation of a vertebral block may be favoured by Paget's disease localized in the vertebral column. This is a little recognized idea even though it was formulated in Schmorl's work at the beginning of this century.