The interaction of hydrogen (H) with lithium (Li) and zinc vacancies (V Zn ) in hydrothermally grown n-type zinc oxide (ZnO) has been investigated by positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry. Li on Zn-site (Li Zn ) is found to be the dominant trap for migrating H atoms, while the trapping efficiency of V Zn is considerably smaller. After hydrogenation, where the Li Zn acceptor is passivated via formation of neutral Li Zn -H pairs, V Zn occurs as the prime PAS signature and with a concentration similar to that observed in nonhydrogenated Li-poor samples. Despite a low efficiency as an H trap, the apparent concentration of V Zn in Li-poor samples decreases after hydrogenation, as detected by PAS, and evidence for formation of the neutral V Zn H 2 complex is presented.