Many treatments for postmenopausal osteoporosis with proven efficacy in lowering fracture risk had become available since many years now. In the last few years the issue about treatment duration has become a matter of importance. In this paper the pivotal trials for alendronate, risedronate, zoledronate and other anti reabsorptive drugs such as denosumab are revised with particular attention to the extension studies aimed to verify the effect of drug discontinuation. The results of the review highlight differences among the available drugs and the practical clinical consequences also in terms of cost-effectiveness.