This study assessed the mandibular foramen (MF) position variability in dentate and edentate Brazilian mandibles. Eighty dentate and 79 edentate mandibles of unknown sex were measured bilaterally using a digital caliper (0.1-mm precision). Horizontal linear measurements (HM) were done from the MF to the anterior border of the mandibular ramus (MF-A) and from the MF to the posterior border of the mandibular ramus (MF-B). Vertical linear measurements (VM) were done from the MF to the most inferior point of the mandibular notch (MF-C) and from the MF to the inferior border of the mandibular ramus (MF-D). Data were analyzed by two-way ANOVA (alpha = 5%). The HM means and standard deviations (±SD) for MF-A were, edentate right (ER): 17.5 (±3.2) mm, edentate left (EL): 17.4 (±3.4) mm, dentate right (DR): 19.2 (±3.6) mm, and dentate left (DL): 18.8 (±3.8) mm. The means (±SD) for the MF-B measurements were, respectively, ER: 12.8 (±2.4) mm, EL: 12.9 (±2.3) mm, DR: 14.2 (±2.4) mm, and DL: 13.9 (±2.6) mm. The VM values for the MF-C measurements were, ER: 23.4 (±3.8) mm, EL: 22.9 (±3.7) mm, DR: 23.6 (±3.1) mm, and DL: 23.1 (±3) mm, and for the MF-D measurements, ER: 26.4 (±4.2) mm, EL: 26.4 (±4) mm, DR 28.3 (±3.9) mm, and DL 28 (±3.8) mm. Side had no influence (p>0.05) on any edentate or dentate mandible measurement. Dentate mandible measurements showed statistically significant differences compared to the edentate mandibles, except for MF-C. The mandibular foramen position changes with loss of teeth and this variability may be responsible for occasional failure of inferior alveolar nerve block. Clin. Anat. 23:394–398, 2010. © 2010 Wiley-Liss, Inc.