The relationship between mandibular bone mass and tooth loss was studied in 269 patients who had neither metabolic disease nor local lesions affecting the mandibular cortex. In all of the subjects, the outline of the mental foramen was distinctly disclosed on unilateral or bilateral panoramic radiographs. Mandibular bone mass was evaluated by determining the mandibular cortical width in the mental region with the use of panoramic radiographs. The relationships of mandibular cortical width to patient age and sex and the number of teeth present were also investigated. In male subjects, there was no significant correlation between the number of teeth present and the mandibular cortical width. Among women in their seventh decade, those with 15 or more teeth showed significantly greater mandibular cortical width than those with fewer teeth. Decrease of mandibular bone mass was positively correlated with tooth loss in female subjects.