We analyzed forty-four patients who had osteogenesis imperfecta, in order to determine the prevalence of spinal deformities. At the time of the most recent follow-up, scoliosis was present in thirty patients (68 per cent) and kyphosis, in eighteen (41 per cent). According to the classification system of Falvo et al., scoliosis progressed rapidly with growth in twelve of fifteen patients who had the congenita type of osteogenesis imperfecta and in four of thirteen who had the tarda-I type. Curves that progressed before puberty did not always continue to progress after cessation of growth. Lateral roentgenograms made at the initial examination revealed four types of vertebral body deformities: biconcave, flattened, wedged, and unclassifiable vertebrae. Biconcave vertebrae were seen characteristically in patients who had the congenita type of osteogenesis imperfecta. The presence of six biconcave vertebrae or more before puberty indicated that severe scoliosis (more than 50 degrees) was likely to develop. Biconcave vertebrae did not appear to affect the severity of kyphosis. The other types of vertebral deformities were not useful for predicting progression of spinal deformity.