The vibrational spectra and positions of H(D) atoms in NbC1−yHx(Dx) (0.19 ≤ y ≤ 0.29, 0.04 ≤ x ≤ 0.30) have been studied by inelastic neutron scattering (INS) and neutron diffraction. The analysis of the neutron diffraction data for NbC0.76Hx(Dx) and NbC0.71Hx(Dx) has revealed a number of different structures depending on the carbon concentration and the presence of absorbed H(D) atoms: the partially ordered cubic Pm3¯ m structure for NbC0.76, the partially ordered orthorhombic Pmmm structure for NbC0.76D0.17 and NbC0.76H0.18, the disordered cubic Fm3¯ m structure for NbC0.71 and NbC0.71D0.30, and the disordered tetragonal I4/mmm structure for NbC0.71H0.28. The INS spectra of NbC0.81Hx and NbC0.76Hx(Dx) in the energy transfer range 40–140 meV are found to consist of a single fundamental peak due to hydrogen optical vibrations (centered at 98 meV for H and at 65 meV for D) and a single peak due to carbon optical vibrations (centered at 78 meV). In addition to these peaks, the INS spectrum of NbC0.71H0.28 exhibits a peak at 130 meV, suggesting that H atoms in this compound occupy the sites displaced from the centers of carbon vacancies.