[en] In this paper, we present the electron-impact ionization cross sections for eight highly charged Na-like ions in the range 18≤Z≤39 calculated by means of a distorted-wave Born exchange approximation method including relativistic corrections. Direct ionization from the ground and excited states (n=3-5) is calculated. For the ground state, contributions due to excitation-autoionization are also calculated, taking account of branching ratios and configuration interaction. A systematic study of the dependence of the cross sections on impact energy and nuclear charge is carried out for the direct ionization of all states and for excitation-autoionization. The results of the calculations are fitted by empirical formulas to facilitate use in practical applications; the fitted values are found to be in good agreement with the calculated results. An accurate empirical formula for calculating ionization rates is also given