18 F-fluoride Positron emission tomography (PET) is able to demonstrate and quantify the metabolic activity locally in the skeleton (1). This technique should, therefore, also be able to demonstrate a dramatic decrease in the metabolic activity in localized monostotic Paget’s disease lesions after therapy. In this condition, indeed, the usual biological markers may be unhelpful to assess the efficacy of therapy, because they are usually comprised in the normal range for single pagetic localizations, even before therapy (2). The main purpose of this trial is to assess the early and long term response of pagetic bone to bisphosphonate therapy.