The powder neutron diffraction pattern of pyrolusite, β-MnO2 [P42/mnm, No. 136, a = 4.4041(1), c = 2.8765(1)Ǻ], has been refined by the Rietveld method to give values for both the oxygen position parameter u=0.3046(1) and the anisotropic thermal parameters. The data confirm the MnO6 octahedra to be elongated with two long [1.894(1)Ǻ] and four short [1.882(2)Ǻ] Mn-O bond distances. The effect of the stereochemistry on the thermal vibrations is discussed.