It has become an axiom that the thermodynamic analysis of non-covalent molecular complexation is intrinsically model-dependent, i.e. the set of implicitly or explicitly introduced assumptions may strongly affect the thermodynamic parameters. This review deals with the entropy change accompanying molecular complexation, which results in the formation of ordered structures. In simple terms the key question may be formulated as follows: 'If the molecular complexation leads to the formation of supramolecular structures, then, the system entropy changes due to ordering. So, how is this factor accounted for in standard models of molecular complexation and does it have any effect on the magnitude of measured thermodynamic parameters of complexation?' The structure of the review is made as a collection of cases in which the hidden entropy change has been recognized among the most influential factors.