The basis set superposition error (BSSE) of hydrogen-bonded trimers, (NH3)(3), (H2O)(3), (HF)(3), (PH3)(3), (H2S)(3) and (HCl)(3), was examined using the Counterpoise (CP) approach at the MP2 level with various basis sets. Trimers from periods 1 and 2 elements showed a similar trend in the geometrical variations, even though the CP-corrections on the interaction energies of the latter were much larger. The degree of the changes in the bond length was not significant when a sufficiently large basis set was used. The CP-correction function, delta E(fCP), made a considerable contribution to the complexation energy, Delta E-c, even with the largest basis set. (C) 2012 Elsevier B.V. All rights reserved.