A condition characterized by extreme loss of bone mineral density (thickness) that leads to a markedly increased risk of fracture. It is primarily diagnosed by a bone mineral density exam/DXA. It addition to calcium and vitamin D treatment it almost always requires treatment with bisphosphonates (Fosamax/Actonel/Boniva), denosumab (Prolia), or, in the case of recent fracture, Forteo. Untreated, hip, back and wrist fractures have a high risk of causing loss of independence, disability, or even death.