Because there are now effective agents for treatment of osteoporosis, the question is being raised as to whether or not it is ethical to have placebo-controlled trials of new agents. It is ethical for patients who are at low risk of serious or irreversible harm to participate in placebo-controlled trials as long as they provide informed consent. Morbidity, mortality, and future fracture risk correlate with the presence of previous fractures, the number of previous fractures, whether or not the fracture is recent, and whether or not the fracture is clinically recognized. Lower-risk subjects who may be allowed to participate in placebo-controlled trials include those with low bone density but without a previous vertebral fracture, those with a single vertebral deformity that was not clinically recognized, and those with a vertebral fracture more than 2 years before. Higher-risk subjects who do not tolerate proven drugs or who have not responded to proven drugs may also participate. Even though it may be ethical for selected subjects to participate in placebo-controlled trials of new therapies for osteoporosis, steps should be taken to minimize their exposure (eg, unbalanced randomization, integration of outcomes, and powering trials to actual events rather than a projected number over 3 years), and treating patients who fracture or who fail to respond.