The p-aminobenzoic acid (C7H7NO2) molecule has been investigated at different levels of theory. DFT methods (B3LYP and PBE1PBE), second order Moller-Plesset perturbation theory (MP2) and composite ab initio methods (G3MP2 and CBS) have been employed, in conjunction with large basis sets. Important informations on the electronic structure and thermochernistry of this molecule have been extracted, and the performance of the density functional and ab initio methods has been evaluated, based on the comparison of the calculated and the available experimental data. (C) 2007 Elsevier B.V. All rights reserved.