The endolymphatic sac (ELS) and vestibular aqueduct (VA), which play a notable role in the pathogenesis of endolymphatic hydrops and Meniere disease, were identified in all anatomic and tomographic materials. More than 100 temporal bones were used for microdissection, tomography, and plastic molds. Normal subjects and Meniere disease patients were studied tomographically (N = 63) and observed during ELS surgery (N=49). In Meniere disease there is, with increassing duration of diseases, a decrease in the periaqueductal and opercular air cell pneumatization, with a concomitant shorter and straighter VA. This correlates with a decreased ELS luminal patency, and a more inferiorly positioned ELS. These factors help to explain both the difficulties of visualizing the VA by tomography in Meniere disease as well as the occasional difficulties reported by others in satisfactorily identifying the ELS at sac surgery. All observations are made from the surgeon's viewpoint to enhance clinical identification of the ELS.