Observational constraints on the primordial lithium abundance are important for the evaluation of the baryonic density of the universe .
Its precise determination however suffers from uncertainties due to the possible depletion of this element inside the stars .
Here we present and discuss new results on the lithium abundances in Pop II stars obtained with most recent stellar models including the best available physics .
We show that it is possible to account for the general behavior of lithium observed in Pop II stars without any free parameters .
Macroscopic motions inside the stars are needed but it is not necessary to specify their exact nature to interpret the observational data .
This constatation allows to derive a parameter-free value for the lithium primordial abundance : \log { Li } _ { p } = 2.35 \pm . 10 in the \log { H } = 12 scale .