The structure of Sr 2 RuO 4 has been studied by means of neutron single-crystal diffraction as function of temperature. The analysis of the anisotropic atomic displacement parameters (ADP) and the non-existence of superstructure reflections allow one to exclude structural deformations similar to those occurring in Sr 2 IrO 4 and La 2 CuO 4 , for short and long range order type. Furthermore, we find no indication for an anomaly in the temperature dependence of the RuO 6 octahedron elongation near 140 K where extrema in the resistivity have been reported.