In 43 edentulous, lower jaw halves, sections were carried out in the area between the mental foramen and the third molar. The relative changes in the location and course of the mandibular canal which are caused by atrophy were analysed. For this purpose, the mandibles were classified according to so-called residual ridge orders which describe the different stages of alveolar ridge resorption. The following findings were obtained: The distance between the mandibular canal and the lingual and buccal external border does not change in any stage of the atrophic process, i.e. it remains conspicuously constant. However, the distance between the mandibular canal and the cranial and caudal borders of the body of the mandible partly changes to a statistically highly-significant extent, the distance between the canal and the atrophic alveolar ridge being affected more strongly than that between the canal and the base of the mandible. These changes were most clearly pronounced in the area of the first molar.