Introduction The presence of an eroded or thinned cortex of the mandible on panoramic radiographs may be useful in identifying women with osteoporosis. However, little is known as to whether a non-eroded thin cortex predicts osteoporosis. Objective To clarify whether visual assessment of non-eroded thin cortex increases the diagnostic efficacy of identifying women with osteoporosis. Materials and methods Of 60 observers who participated in OSPD (Taguchi et al., Bone, 2008), 41 observers visually assessed non-eroded thin cortex in addition to Klemetti’s index (KI) for 100 panoramic radiographs on the OSPD website via the Internet twice with approximately a two-week interval. The area under the receiver operating characteristics curves (AUROC) in identifying women with osteoporosis by both KI and non-eroded thin cortex was calculated on two occasions; non-eroded thin cortex was included in “class 1 of KI (decreased probability of osteoporosis)” or “class 3 of KI (increased probability of osteoporosis)”. Mean AUROC was compared between these two occasions with paired ttest. Results In the first series of observations, the mean AUROC significantly increased when noneroded thin cortex was considered as a sign of increased probability of osteoporosis (mean +/- SD, 0.68 +/- 0.08 vs. 0.70 +/- 0.07, P=0.011). In the second set of observations, the result was unchanged (0.68 +/- 0.09 vs. 0.71 +/- 0.08, P<0.001). Conclusions and discussion Visual identification of a non-eroded thin cortex on panoramic radiographs may increase the diagnostic efficacy of identifying women with osteoporosis.