A brief review of the basis for equations of state for complex fluids is presented. Particular emphasis is placed on extensions of a theory due to Wertheim. These extensions are the basis for the successful SAFT equation of state. We combine these extensions with a new theory for intramolecular hydrogen bonding to study the effect of the competition between intermolecular and intramolecular hydrogen bonding on the thermodynamic properties of polyatomics. Comparisons with molecular simulation results are presented to demonstrate the accuracy of the theory. By considering the limit of complete intramolecular association, an accurate equation of state of cyclic molecules is obtained.