The needlelike morphology of aspartame form II-A is studied by means of Monte Carlo simulations. Growth simulations for all F faces show merely three faces with a nucleation barrier for growth: two side faces and one top face. Calculations of the energies involved in the growth for a few representative faces are in good agreement with these observations. For two of these faces, nuclei or steps could be formed without any energy cost. The simulations explain the needle shape of aspartame crystals and also the high supersaturation needed to nucleate the crystals.