Fifty subjects with amelogenesis imperfecta were investigated clinically and with cephalometric radiography in order to determine the prevalence and nature of the anterior open-bite, which has been reported in association with these enamel defects. Anterior open-bite occurred in 24 percent of the subjects and was always associated with a severe discrepancy in the vertical relationship of the jaws. This vertical dysgnathia also occurred in a further 20 percent who did not have anterior open-bite. It is suggested that the frequent association of anterior open-bite and amelogenesis imperfecta is caused by a genetically determined anomaly of craniofacial development, rather than by local factors influencing alveolar growth.