Complex thermochemistry modeling in the wake of a detonation or shock propagation requires accurate equations of state (EOS) for the resulting chemical species under high temperature and pressure. Nitrous acid (HONO or HNO2) has been shown to be an important post-detonation product for many energetic compounds. Given that its EOS has not been determined so far, either experimentally or theoretically, we develop a class II force field to model both conformers (i.e. cis and trans) of HONO, and compute the EOS using classical molecular dynamics simulations. We then show that this EOS can be well represented within a thermodynamics theory framework previously applied to other polar fluids. (C) 2008 Elsevier B. V. All rights reserved.