We have shown that the main factors affecting the equilibrium constant of self-association of aromatic molecules during the growth of an aggregate are the loss of translational and rotational degrees of freedom on the formation of a complex, the ordering of molecules (the entropy of mixing) into aggregates, and the electrostatic interaction (if molecules possess a charge). On the basis of these ideas, we have first obtained the formula for the equilibrium constant of self-association of aromatic compounds as a function of the number of molecules in the aggregate and drawn conclusion that, in the frame of the model in use, the profile of the constant is decaying.