Starting from explicitly correlated wavefunctions, the one-body momentum de
nsity, gamma ((p) over right arrow), and the expectation values [delta((p)
over right arrow)] and [p(n)], with n = -2 to +3, have been obtained for th
e atoms helium to neon. All the calculations have been carried out by using
the Monte Carlo algorithm. An analysis of the numerical accuracy of the me
thod has been performed within the Hartree-Fock framework. The effects of t
he electronic correlations have been systematically studied by comparing th
e correlated results with the corresponding Hartree-Fock ones.