The interplay between two important noncovalent interactions involving aromatic rings is studied by means of ab initio calculations (RI-MP2(full)/6-31++G**) computing the genuine non-additivity energies. They demonstrate that cooperativity effects are present in complexes where cation-pi and hydrogen bonding interactions coexist. Interestingly the non-additivity energies are monotonically incremented by growing the number of hydrogen bonds. These non-additivity effects have been studied using the 'atoms-in-molecules' theory and the Molecular Interaction Potential with polarization partition scheme. (C) 2009 Elsevier B.V. All rights reserved.