Monte Carlo simulations of a three-dimensional lattice model of an amphiphile-solvent system are presented and examined for their usefulness in predicting the thermodynamics of self-association of amphiphiles in solution, The size distribution of the aggregates obtained from the simulations is used-in combination with the mass action model-to obtain the thermodynamic properties of the solution of aggregates and to obtain expressions for the coefficients of an empirical equation for the Gibbs energy available in the literature for aqueous nonionic surfactant solutions. The results are in good agreement with the empirical model, and the essential microstructural features and thermodynamic properties of the micellar solution can be extracted reasonably well using such an empirical fitting of the simulation data. The effects of the lengths of the solvophobic and solvophilic sections of the amphiphile on critical micelle concentration extracted from the simulations are consistent with experimental results reported for several nonionic surfactants in water.