PURPOSE: If damage to the neurovascular bundle of the mandibular canal during dental implant surgery of the mandible is to be prevented, accurate measurement of the distance between the alveolar crest and the mandibular canal, as seen on panoramic radiographs, is important. The purpose of this study was to compare the accuracy of panoramic radiography using a lead ruler with that of computed tomography for the measurement of the distance between the alveolar crest and superior border of the mandibular canal and to evaluate the usefulness of panoramic radiography using a lead ruler. MATERIALS AND METHODS: For control study, panoramic radiography of the dry mandible was undertaken using a lead ruler, and computed tomography was added. The distances between the alveolar crest and the superior border of the mandibular canal and between the alveolar crest and the lowest border of the body of the mandible were measured at the level of the 2nd premolar to the 3rd molar. These measurements were compared with actual measurements of the dry mandible in the same areas. The cases of 87 patients[49 men, 38 women; age range, 20 -84 (mean, 42) years] who had undergone panoramic radiography using a lead ruler were reviewed. They were catergorized according to sex, the presence of teeth, and whether under or over 50 years of age. All measurements were compared and analyzed using the Student t-test. RESULTS: Measured values obtained from a panoramic radiograph using a lead ruler(magnification:100.32%+/-5.92) and from a computed tomograph(magnification:100.22%+/-5.55) deviated less from actual measurements on the dry mandible (p > 0.05). The distance from the 2nd premolar to the 3rd molar was greater in male adults (19.62 mm +/-3.95) than in female (17.54 mm +/-4.04) (p < 0.05), except the 3rd molar. In addition, the distance was greater in dentulous patients(18.81 mm +/-3.33) than in edentulous (16.23 mm +/-1.75)(p < 0.05), except the 3rd molar. There was, howerer, no significant difference between patients under and over 50 years of age (p> 0.05), except 2nd pre molar and 1st molar in the female. CONCLUSION: Panoramic radiography using a lead ruler is a simple and accurate modality for the presurgical planning of dental implant surgery. It is suggested that the successful long-term rate of dental implantation may be higher in dentulous male than in edentulous female molars.