The dispersion relations for phonons in solid ortho-deuterium have been measured at 5 °K by inelastic neutron scattering. The results are in good agreement with recent calculations in which quantum effects are taken into account. The data have been fitted to a third-neighbor general force model. The effective force constants which are obtained show that the bond stretching forces between nearest-neighbor molecules are dominant and this bond stretching constant is 174 dyn cm-1. The elastic constants are deduced and the isothermal compressibility is calculated to be B-1=2.19×10-10 cm2 dyn-1. The density of states and the heat capacity is calculated and the Debye temperature is found to be θ0=114 °K.