First principles calculations of the structural, thermodynamic, electronic and vibrational properties of C1b-NiTiSn half-Heusler compounds have been performed. The enthalpy of formation of C1b-NiTiSn has been obtained. The phonon density of states has allowed to derive a value of the Debye temperature of the compound. The enthalpies of formation of point defects have been calculated using large supercells. Four sublattices have been introduced to account for the C1b structure and for the possibility of inserting atoms in the 4d Wyckoff positions of the F4 3m structure. The most stable defects are INi and VNi. The corresponding densities of states have been computed.