The external aperture width of the vestibular aqueduct was measured in living subjects of various ages, with normal and diseased ears. Measurements were made from 3-dimensional reconstruction of CT images, and the developmental process was studied. The following results were obtained. i) In Menière's disease the external aperture was hypoplastic and its width significantly smaller than that in normal individuals and those with chronic otitis media, including children. ii) There were no significant differences between normal ears and ears with chronic otitis media in either adults or children. The development of external aperture was completed in childhood. iii) In Menière's disease, hypoplasia evidently begins before childhood, which suggests that congenital factors are involved in the pathology of this disease.