Thermal, structural, and vapor-liquid equilibrium properties for a site-site potential model of methyl iodide have been studied using NPT and Gibbs ensemble Monte Carlo simulations. Densities and enthalpies of vaporization are in very good agreement with experiment over a wide range of thermodynamic conditions. The structure reflects competition between antiparallel and linear;dimers and suggests that dipolar interactions play an important role in liquid methyl iodide. The critical properties have been estimated by fitting the Gibbs ensemble Monte Carlo results to the laws of rectilinear diameters and order parameter scaling. The estimated values were T-c = 548.6 K and rho(c) = 0.735 g cm(-3), in good agreement with the experimental values 528 K and 0.747 g cm(-3), respectively. The influence of the Coulombic long-range corrections on the vapor-liquid coexistence and critical properties has been analyzed by performing simulations with and without Ewald sums. In order to discuss the importance of the Coulombic interactions; a site-site Lennard-Jones system has also been analyzed.