Vertebral fractures are the most common but least understood of all osteoporotic fractures. Their study has been hampered by the lack of a common morphometric definition, and the fact that many vertebral fractures are asymptomatic and not clinically evident. Population-based radiographic surveys are therefore required for comparative studies. Risk factors fall into five major categories:​ (1) age, or age-related, (2) genetic, (3) environmental, (4) endogenous hormones or chronic diseases, and (5) physical characteristics of bone. Bone density is the most clinically useful risk factor, particularly for purposes of prevention. Because vertebral fracture prevalence parallels levels of bone density, bone density is also useful for epidemiological surveys. Based on WHO diagnostic criteria, 54% of postmenopausal white women in the United States have osteopenia, and another 30% have osteoporosis. Existing fractures are also strong, independent predictors of future vertebral fracture risk, but also represent a later, and less treatable, stage of the disease.