We show that there is a wide range of problems, where high accuracy astrometry can bring new information in stellar evolution, not limited to the classical applications in the HR diagram, such as the determinations of the helium and metal contents and of the size of the convective core. In particular, we show some new applications to the study of star formation. The accurate measurement of the luminosity of the observed birthline in the HR diagram is a key information very sensitive to the mass accretion rates. These rates determine all the properties of the pre-MS models. For the evolution of massive stars with mass loss and rotational mixing, strong constraints can be obtained from the combination of astrometric data and abundance determinations obtained by high resolution spectroscopy. We also emphasize that a better knowledge of the luminosity distribution of WR stars is strongly constraining the final masses at the time of supernova explosions as well as the nucleosynthetic yields.