Bisphosphonates are currently used in the therapy of osteogenesis imperfecta (OI) to decrease the bone fragility observed in OI patients. Bisphosphonate therapy delays tooth eruption in rats. The aim of this study was to determine whether or not bisphosphonate therapy delays tooth eruption in children. The clinical emergence of teeth was observed and the calculated dental age and the number of delayed teeth were determined for 33 OI patients treated with bisphosphonates and for strictly gender- and age-matched controls. There were significant differences between bisphosphonate-treated patients and controls for calculated dental age and number of delayed teeth. Bisphosphonate therapy was associated with a mean delay of 1.67 yr in tooth eruption in children with OI.