Objective: Osteoporosis has become a critical public health problem with the rapidly aging population in Japan. It is necessary for dentists to know their patients' status because it influences dental treatment. The purpose of this study was to predict the risk of osteoporosis in elderly patients visiting a dental clinic by assessing mandibular cortical morphology on panoramic radiographs. Method: Three-hundred and thirty patients were divided into three classes based on the morphology of their mandibular cortex on panoramic radiographs. Mandibular cortical bone width at the mental foramen was also measured. Bone mineral density (BMD) was determined at the calcaneus using a quantitative ultrasound device. Results: The mandibular cortical width decreased significantly from Class 1 (normal cortex), to Class 2 (moderately eroded cortex) and to Class 3 (severely eroded cortex). BMD was negatively correlated with age in both female and male patients. Most (108/186) female patients had a class 3 cortex with a low BMD. Among women, mandibular cortical width was significantly correlated with BMD. Thirty-three percent of the female had received a previous diagnosis of osteoporosis. In contrast, only 13.9% (20/144) of the male had a Class 3 cortex. In men, mandibular cortical width did not significantly correlate with BMD. Only a few of the men had received a previous diagnosis of osteoporosis. The number of remaining teeth did not correlate with low BMD in either sex. Conclusion: Our findings reveal that most elderly female patients visiting the dental clinic had a high risk of osteoporosis and a low BMD.