We report a numerical study of the structure and phase behavior of a model for a triblock-copolymer solution. The aim of this study is to investigate the nature of the dense micellar phase that can form in such systems. The simulations were performed on a lattice model for PEO (poly(ethylene-oxide))-PPO (poly(propylene-oxide))-PEO polymers. At high volume fractions, the structure factor of the amphiphile-solvent system can be mapped onto that of a monodisperse hard-sphere fluid. Yet, a low-density hard-sphere model cannot account for the properties of the dilute micellar solution. Moreover, direct inspection of the snapshots of the suspension show that these model triblock-copolymer micelles are neither hard, nor spherical, nor monodisperse. (C) 2004 American Institute of Physics.