One of the most important purposes in molecular technologies is the preparation of supramolecular structures by self-assembling processes. The aromatic molecules self-associate mainly in pi-pi stacked structures with an aggregate size distribution determined by the association equilibrium constants. A general expression for the equilibrium constants K-n,K-m which govern the self-association of two aggregates with n and m monomers respectively has been obtained. The model predicts also the concentrations of free monomers, the concentrations of n-mers, and the total concentration of aggregates. H-1 NMR experiments have been used to illustrate the applicability of the proposed model in a particular case: pi-stacking self-association of ciprofloxacin in solution.