Equilibrium molecular dynamics calculations have been performed for the liquid crystal molecule n-4-(trans-4-npentylcyclohexyl)benzonitrile (PCH5) using a fully atomistic model. Simulation data has been obtained for a series of temperatures in the nematic phase. The rotational viscosity co-efficient gamma(1), has been calculated using the angular velocity correlation function of the nematic director, n, the mean squared diffusion of n and statistical mechanical methods based on the rotational diffusion co-efficient. We find good agreement between the first two methods and experimental values. (C) 2002 Published by Elsevier Science B.V.