Developments in electronic structure calculations and computer performances have made it possible to perform ab-initio calculations of structural properties of materials, like defect parameters in transition metals. The values of vacancy formation and migration enthalpies calculated in this context agree with experimental data within less than 10% . Reliable self-diffusion coefficients for the vacancy mechanism can be deduced. This approach sheds new light on the so-called self-diffusion anomaly in body centred cubic metals.