Objective: The purpose of this study was to locate the mandibular canal in relation to the impacted mandibular third molar by conventional cross-sectional tomography. Method and materials: Conventional axially corrected cross-sectional tomograms of 347 successive impacted mandibular third molars of 234 patients referred for removal of the impacted teeth were acquired with a Scanora x-ray unit. The images were assessed for location of the mandibular canal and the impacted mandibular third molar. Descriptive analysis was performed. Results: Examination of the tomograms revealed the alveolar nerve to have, in relation to the mandibular third molar, a lateral (buccal) course in 53.6% (n = 186), a course between the roots in 26.8% (n = 93), a lingual course in 13.0% (n = 45), and an inferior course in 6.0% (n = 21). Supplementary canals were found in 6.3% (n = 22). Two of the tomograms (0.6%) could not be evaluated, in 1 case because of incorrect patient positioning, resulting in an incorrectly adjusted transverse cut, and in the other case because of a mandibular Carcinoma. Conclusion: Conventional axially corrected crosssectional tomograms offer additional information in cases where there is a dose relationship between impacted third molars and the alveolar nerve (superimposition of the roots and the canal, grooving, or a varied direction of the canal on the panoramic radiograph) and may contribute to a higher level of intrasurgical safety. Palabras clave: conventional tomography, impacted mandibular third molar, mandibular nerve, Scanora