Calcium homeostasis is stressed considerably during pregnancy and lactation. Important regulatory mechanisms are needed both for meeting the fetal requirement for calcium and for protecting the maternal skeleton from excessive resorption. For the past 10 years, more and more publications have deal with the involved mechanisms of regulation. The authors have reviewed these publications and tried to answer important questions: is there some irreversible bone loss related to pregnancy and/or lactation? How can such bone loss could be prevented?