Cooperativity in hydrogen bonding has been repeatedly invoked in the literature. Very often a distinction is made between the association constant for the "dimer" formation and the corresponding constant for the formation of association complexes beyond dimer. This work examines this cooperativity hypothesis and proposes a straightforward manner of integrating it in the framework of the lattice-fluid hydrogen-bonding (LFHB) equation-of-state model. This integration is done without altering the basic rationale of the LFHB model for the enumeration of hydrogen bond configurations for the self-association and cross-association in the system. The model can accommodate hydrogen bond cooperativity in complex systems, even polymer mixtures forming three-dimensional networks of hydrogen bonds, and permits its study over an extended range of temperatures and pressures. As additional examples of the applicability of the method, the formation of cyclic associates and of intramolecular hydrogen bonds is also examined.