Dual energy X-ray absorptiometry (DXA) has been widely used in Japan. In this article, we described our lateral measurement of lumbar vertebral body, and reviewed the fracture threshold and the diagnosis of osteoporosis. The bone mineral density was measured in the anteroposterior projection (L2-4BMD) and in the lateral projection (L3 latBMD) by XR-26. The precisions (coefficient of variation) of lateral measurement in lateral decubitus position were 1.73% in BMC, 1.86% in BMD, and 0.82% in Area. The L31atBMD decreased at earlier age than L2-4BMD and showed a significant decrease between the 40s and the early 50s in healthy women as L2-4BMD. The lateral measurement of vertebral body was a very useful method to evaluate the early trabecular bone loss.