Despite the wide availability of bisphosphonate drugs that reduce fracture risk, treatment rates have fallen, attributable to concerns for atypical femoral fractures and osteonecrosis of the jaw. While risk/benefit ratios of bisphosphonate treatment for osteoporosis remain highly favorable in the first 3-5 years, fracture-prevention benefit wanes with longer treatment and risks of side effects increases. This study will estimate the risks/benefits of bisphosphonate drug holidays; determine the cost effectiveness of continuing vs discontinuing a bisphosphonate after 3 years; and develop and validate a risk factor calculator to guide decisions about length of bisphosphonate use.