The crystal structure of rutile-type magnesium deuteride,, has been studied by in situ neutron powder diffraction at room temperature and pressures up to 9.3 GPa. The bulk modulus B0 = 49(2) GPa is about half, the linear compressibilities (0.0063/GPa along a and 0.0041/GPa along c) are about twice and the variation of the free positional parameter x about six times the values for the isostructural magnesium fluoride, indicating the strong polarizability of the deuteride anion. Under pressure the MgD₆ octahedra are more compressed (four Mg––D distances at 199(1), two at 173(1) pm) than at ambient pressure (195.1(1), 194.8(2) pm) and the structural arrangement becomes more CaCl₂ like, although no structural phase transition has been observed