  The calculation of transport properties of Fermi liquids, based on the
formalism developed by Abrikosov and Khalatnikov, requires the knowledge of the
probability of collisions between quasiparticles in the vicinity of the Fermi
surface. We have carried out a numerical study of the shear viscosity of pure
neutron matter, whose value plays a pivotal role in determining the stability
of rotating neutron stars, in which these processes are described using a
state-of-the-art nucleon-nucleon potential model. Within our approach medium
modifications of the scattering cross section are consistently taken into
account, through an effective interaction obtained from the matrix elements of
the bare interaction between correlated states. Inclusion of medium effects
lead to a large increase of the viscosity at densities larger than $\sim 0.1$
fm^{-3}.
