The natural history of the radiographic changes associated with osteogenesis imperfecta was recorded for sixty-four patients. Detailed clinical data regarding spinal deformities were available for forty-three patients. The patients could be placed in six well defined groups on the basis of a cluster of radiographic changes. The radiographic criteria used to classify patients who had osteogenesis imperfecta included the shape, dimensions, and appearance of the long bones; the presence of a trefoil pelvis and protrusio acetabuli; and the shape of the vertebrae. Patients can be classified more accurately if the dynamic nature of the radiographic changes is appreciated. Patients who had Type-A disease, a mild form of osteogenesis imperfecta, maintained the contours of the vertebrae. Most had straight long bones except for five patients who had mild bowing. Patients who had Type-B disease had bowed long bones with wide cortices. The pelvis had a normal contour. The vertebral bodies were biconcave, and kyphosis and scoliosis developed. Patients who had Type-C disease had thin, bowed long bones, and protrusio acetabuli developed around the age of ten years. Patients who had Type-D disease had the same findings as those who had Type-C disease, with the additional finding of cystic changes around the knee by the age of five years. The physes closed early, and the cysts disappeared around the age of fifteen. Patients who had Type-C or D disease had development of severe spinal deformities. Patients who had Type-E disease were totally dependent functionally, and spinal deformities developed at a very early age. The long bones appeared to have no cortex. Patients who had Type-F disease had complete disruption of the ribs, which was incompatible with survival. The natural history of scoliosis in the patients who had Type-B, C, D, or E disease was one of progression of the curve. Bracing used in the treatment of scoliosis in one patient who had Type-E disease and five patients who had Type-C disease was unsuccessful. Arthrodesis of the spine prevented progression of the spinal deformities in patients who had Type-A disease, but the results of the operation were variable in the remaining types of the disease.