The density and temperature dependence of the shear viscosity of liquid sodium is studied. The stress autocorrelation function is calculated by equilibrium molecular dynamics simulations, which allow us to obtain the value of shear viscosity using the Green-Kubo formula. The Fiolhais potential is used to calculate the interionic interactions, which are validated by comparison between simulation and experimental data along the liquid-gas coexistence curve. The behavior of viscosity over a wide range of the liquid phase of the phase diagram is studied. Along isochoric lines, it presents a minimum, while it monotonically increases along isotherms. An expression is proposed for the viscosity as a function of temperature and density which reproduces our data for liquid sodium at any density in the range [1000-2000 kg m(-3)] and any temperature in the range [700-7000 K]. The validity of the Stokes-Einstein relation over the investigated state points is discussed.