Osteoporosis is a condition marked by weak and brittle bones. People with osteoporosis are more likely to fracture their bones. For many adults, a fracture is the initial presentation of osteoporosis. Eight million women (and 2 million men) have osteoporosis in the United States, and an estimated 44 million Americans have osteopenia, which is low bone density placing them at increased risk to develop osteoporosis and fractures. One in two women and up to one in four men will have a low-impact (fragility) fractures of the spine, hip, pelvis, and wrist in their lifetime. Many fractures that are caused by osteoporosis can be prevented with prompt diagnosis and treatment of osteoporosis.