  We study the charged current Drell-Yan process and we evaluate the proton
parton densities uncertainties on the lepton transverse momentum distribution
and their impact on the determination of the W-boson mass. We consider the
global PDF sets CT10, MSTW2008CPdeut, NNPDF2.3, NNPDF3.0, MMHT2014, and apply
the PDF4LHC recipe to combine the individual results, obtaining an uncertainty
on MW that ranges between +-18 and +-24 MeV, depending on the final state,
collider energy and kind. We discuss the dependence of the uncertainty on the
acceptance cuts and the role of the individual parton densities in the final
result. We remark that some PDF sets predict an uncertainty on MW of O(10 MeV);
this encouraging result is spoiled, in the combined analysis of the different
sets, by an important spread of the central values predicted by each group.
