In order to clarify the allotropic structural properties of TiSi₂ we calculated by means of an ab initio density functional approach the total energies of the C49, C54, and C40 crystal structures of the bulk compound. We found that at T=0 K the C49 structure of TiSi₂ is its most stable phase whereas the C54 structure, which experimentally is considered to be the ground state, is less favorable. Furthermore, by calculating the vibrational properties and the corresponding temperature dependent free energies of the three structures we predict a structural transition from C49 to C54 at about 1100 K. We also demonstrate that point defects as well as stacking faults, which are known to be present in the C49 phase, have no significant influence on the structural stability.