Using the dental panoramic tomogram (DPT) and a nickel stepwedge, the prevalence of mandibular osteoporosis in 99 elderly, edentulous individuals was investigated densitometrically. A site was chosen on each DPT adjacent to the mandibular mental foramen and the optical density measured using a digital densitometer. Each DPT was then independently examined by a radiologist and the patients grouped into those exhibiting osteoporosis and those not. Twenty-seven of the patients exhibited qualitative evidence of osteoporosis on the DPT, using established radiological criteria. A large majority of this group was female (25 individuals, 93 per cent). Of the remaining 72 non-osteoporotic patients, only 32 (44 per cent) were female. There was a significant difference in the quantitative, densitometrically derived measurements of mandibular bone density between the osteoporotic and non-osteoporotic groups. The osteoporotic group had a mean optical density at the mandibular measurement site (mean D = -0.773, s.d. = 0.2) which was significantly different from that of the non-osteoporotic group (mean D = -0.888, s.d. = 0.21), t = 2.432, P less than 0.02. This previously diagnosed difference supports the validity of the densitometric technique. When all 99 patients were studied, the difference between the mean mandibular, equivalent nickel thickness of the males and females was significant (t = 2.32, P = 0.022). This sex difference could not be entirely accounted for by differences in the period of edentulousness or age of males and females.