Osteoporosis is one of the main features of the ageing process and the
cost of health care for osteoporosis-related fractures and their comp
lications is a major incentive for prevention, particularly in develop
ed countries with a continuously ageing population. The earliest strat
egies for prevention in menopaused women were based on the anti-osteoc
lastic effect of hormone replacement therapy. Several epidemiological
studies have provided proof of its efficacy showing that in treated po
pulations, there is a significant reduction in osteoporosis-related fr
actures of about 50%, whatever the site of fracture. Although the effe
cts of hormone replacement therapy in the prevention of post-menopausa
l osteoporosis have been well established, three problems remain. Firs
t, what is the degree of efficacy if replacement therapy is started la
te? Second, what is the effect in patients who have already suffered a
n osteoporotic fracture? Third, and most importantly, what is the opti
mal duration of treatment for effective prevention in a given populati
on particularly at risk of hip fracture? These questions suggest new s
trategies for preventive hormone replacement are needed.