Dihydrogen bonded systems (HBeHHX)-H-... and (H2BHHX)-H-... (X = F, Cl, Br) are studied at the HF, DFT and MP2 levels of theory. Counterpoise (CP) corrections are considered on the whole potential energy Surface (PES) in order to get basis set superposition error (BSSE) free minima. It is shown that the use of CP-corrected PES is necessary in order to obtain a good description of these weak bonds; furthermore, the study reveals that at the MP2 level, the BSSE and the interaction energy are about the same order, so wrong conclusions may be obtained if only the uncorrected PES is considered. (C) 2004 Elsevier B.V. All rights reserved.