The electronic and magnetic properties of the Ti2RuSn Heusler compound are investigated by means of ab initio calculations with the full-potential linearized augmented plane wave (FLAPW) method. The generalized gradient approximation (GGA) method is used for the calculations. The CuHg2Ti-type structure is energetically more stable than the AlCu2Mn-type structure. The inverse-Heusler Ti2RuSn represents half-metallic behavior. The total spin moment of the compound is 2 mu B which coincides with the Slater-Pauling rule of M-t = Z(t)-18 with the equilibrium lattice constant a(0) = 6.44 angstrom and the strained lattice constants as well. The majority bands have metallic properties, but the minority bands have semiconductor properties with a gap of 0.35 eV, and the spin-flip gap is 0.23 eV. Moreover, the sensitivity of half-metallicity is investigated under two types of structural distortion, namely uniform strain and tetragonal distortion.