We present a primitive model for a room-temperature ionic liquid, where the cation is modeled as a charged hard spherocylinder of diameter sigma and length l and the anion is a charged hard sphere of diameter sigma. Liquid-vapor coexistence curves and critical parameters for this model have been Studied by grand-canonical Monte Carlo methods. Our results show a decrease of both the critical temperature and density as the cation length l increases. These results are in qualitative agreement with recent experimental estimates of the critical parameters.