The threshold for pharmacological intervention for osteoporosis remains controversial. Tools predicting the future risk of new fractures are increasingly used to establish a convenient individual risk/benefit ratio for a long term treatment. FRAX® is likely to become the most widely used tool for assessing fracture risk also for the WHO endorsement. The inevitable limitations will not hamper its value. As for any tool like this a continuous process of validation and further development is highly warranted. The predictive and clinical value of FRAX® has to be tested in individual countries by exploring also the inclusion of additional specific relatively uncommon risk factors. The DeFRA project is intended to validate in a large cohort of postmenopausal women a new algorithm derived from FRAX®. Both, the coefficients of continuous variable and the gradients for clinical risk factors should not be considered as conclusive for the routine clinical use. The new tool will be offered for the routine clinical use only at the completion of the DeFRA project, requiring the prospective collection of at least 60.000 patient-years. Here we report the rational and the design of the project.