The Gaussian-2 (G2) ab initio procedure has been applied to gas-phase species of the formulas AlXn+, AlXYn+ and AlXYZ(n+) (n = 0, 1; X, Y, Z = F, Ci, Br). Existing thermochemical values for several of these species are highly uncertain, and many appear not to have been subjected to any previous study. The G2 results reported herein can be assessed against eight aluminum halides (namely AlF, AlCl, AlF+, AlFiCl3-i (i = 0-3), and AlBr3) whose enthalpies of formation are known to an accuracy of +/-10 kJ mol(-1) or better : in all cases, very good agreement is found between G2 and the literature values, while the literature values for several other species of uncertain thermochemistry are found to disagree with the G2, results despite large experimental uncertainties. In particular, we urge further experimental examination of the thermochemistry of AlF2, AlFCl, and AlCl2 and their molecular cations, for which the enthalpies of formation recommended in the JANAF thermochemical tables appear to be systematically too low.