Polytomography permits clear visualisation of the internal auditory meatus (IAM), the normal range of measurements of which is important for radiograph interpretation. Previous reports indicate wide variation in vertical diameter and in the length of the posterior canal wall although in any one individual there is usually little variation between the two sides. We studied the relationship of both the vertical diameter and the length of the posterior walls of the IAM to the growth of the skull and pneumatisation of the temporal bone in 300 patients with no evidence of a lesion of the VIII nerve. No statistically significant correlation was observed between these factors.