Recent interest in cochlear implantation for children has made it important to understand how postnatal growth of the ear will affect such devices. In this study, the postnatal growth of the labyrinth, middle ear, and mastoid was measured in three dimensions using radiographic and temporal bone data. Measurements were made from histologic sections of 48 temporal bones from children and compared to adult temporal bones. Radiographic measurements were made from 253 sets of skull radiographs of children and compared to adult skull series. In the three dimensions measured, there was no postnatal growth of the labyrinth and little variation in size between individuals. Measurements of the middle ear showed greater variation between individuals than measurements of the inner ear, but growth only in the distance from stapes footplate to the tympanic membrane. The mastoid showed growth in all three dimensions: length, width, and depth. The pattern of growth for mastoid length and width appears to follow a double logistic model, with differences between males and females. The growth in mastoid depth is smaller and appears to follow a single exponential curve. The implications for cochlear implantation in children are discussed.