We investigate the effect of interaggregate interactions on the pressure of a micellar system in two dimensions. We consider a simple model that takes into account only hard-core interactions among aggregates. We derive an expression for the pressure of the micellar solution including the contribution of the second-virial correction. The distribution of the aggregates is determined from Monte Carlo simulations on a two-dimensional lattice, where a water molecule occupies a single site, and each amphiphile occupies three sites. The contribution of interaggregate interactions, that become apparent only above the critical micellar concentration, is a small fraction of the ideal gas pressure.