BACKGROUND Spinal deformities are common in patients with osteogenesis imperfecta, a heritable disorder that causes bone fragility. The purpose of this study was to describe the behavior of spinal curvature during growth in patients with osteogenesis imperfecta and establish its relationship to disease severity and medical treatment with bisphosphonates. METHODS The medical records and radiographs of 316 patients with osteogenesis imperfecta were retrospectively reviewed. The severity of osteogenesis imperfecta was classified with the modified Sillence classification. Serial curve measurements were recorded throughout the follow-up period for each patient with scoliosis. Regression analysis was used to determine the effect of disease severity (Sillence type), patient age, and bisphosphonate treatment on the progression of scoliosis as measured with the Cobb method. RESULTS Of the 316 patients with osteogenesis imperfecta, 157 had associated scoliosis, a prevalence of 50%. Scoliosis prevalence (68%) and mean progression rate (6° per year) were the highest in the group of patients with the most severe osteogenesis imperfecta (modified Sillence type III). A group with intermediate osteogenesis imperfecta severity, modified Sillence type IV, demonstrated intermediate scoliosis values (54%, 4° per year). The patient group with the mildest form of osteogenesis imperfecta, modified Sillence type I, had the lowest scoliosis prevalence (39%) and rate of progression (1° per year). Early treatment-before the patient reached the age of six years-of type-III osteogenesis imperfecta with bisphosphonate therapy decreased the curve progression rate by 3.8° per year, which was a significant decrease. Bisphosphonate treatment had no demonstrated beneficial effect on curve behavior in patients with other types of osteogenesis imperfecta or in patients of older age. CONCLUSIONS The prevalence of scoliosis in association with osteogenesis imperfecta is high. Progression rates of scoliosis in children with osteogenesis imperfecta are variable, depending on the Sillence type of osteogenesis imperfecta. High rates of scoliosis progression in type-III and type-IV osteogenesis imperfecta contrast with a benign course in type I. Bisphosphonate therapy initiated before the patient reaches the age of six years can modulate curve progression in type-III osteogenesis imperfecta.