Bone mineral density (BMD) measurement using dual-energy X-ray absorptiometry (DXA) is a key contributor to the management of bone fragility syndromes, most notably postmenopausal osteoporosis. Experimental studies of bone biomechanics have established that an accurate marker for mechanical strength is areal BMD (aBMD, g/cm2). Areal BMD contributes 70% of mechanical strength at the femur and 40% at the spine. Two decades after the T-score was first introduced (World Health Organization, 1994), changes have occurred in the indications of DXA and in the interpretation of its results for the diagnosis, prognosis, and treatment of osteoporosis.