A combination of tandem mass spectrometry experiments (collisional activation and neutralization-reionization mass spectrometry) and ab initio molecular orbital calculations was used to provide evidence for the stability of thionitrosyl hydride, H-N=S, and to characterize it. Experimentally, HNS has been generated using three different precursors. The (HNS) potential energy surface has been explored in the lowest-lying singlet, triplet and doublet ionized states using (PU)MP4/6-311++G(2df,2pd) energies based on (U)MP2/6-31G(d,p) geometries. Predictions for several spectroscopic properties of NHS have been made on the basis of MO calculations and empirical corrections. These include geometry, rotational constants, vibrational wavenumbers, dipole moment, N-14 nuclear quadrupole coupling constant, triplet-singlet energy gap, electron and proton affinities, ionization and pi* <-- n transition energies.