It was suggested as long ago as 1941 that there might be a connection between the menopause and osteoporosis. Since then, abundant data have confirmed that hypothesis as well as showing that such osteoporosis may be prevented by estrogen supplementation (ERT--estrogen replacement therapy). In estrogen deficiency, increased bone resorption takes place in the process of bone remodeling, leading to bone loss. The bone loss occurs universally but to the greatest extent at sites rich in trabecular bone. There are uncertainties concerning extent of bone loss at various sites at different ages, effect of ERT at varying sites and different ages, degree of fracture prevention, and relationship between duration of therapy and fracture risk. That optimal fracture risk is not being attained now on a population basis is due to apparently low acceptance of ERT by patients and lack of strenuous effort in that direction by physicians.