X-ray data on single crystals of the quaternary metal hydride near the composition LiB0.33N0.671H2.67, previously identified as "Li3BN2H8", reveal that its true composition is Li4BN3H10. The structure has body-centered-cubic symmetry [space group I2(1)3, cell parameter a = 10.679(1)-10.672(1) A] and contains an ordered arrangement of BH4- and NH2- anions in the molar ratio 1:3. The borohydride anion has an almost ideal tetrahedral geometry (angle H-B-H similar to 108114), while the amide anion has a nearly tetrahedral bond angle (angle H-N-H similar to 10(6)). Three symmetry-independent Li atom sites are surrounded by BH4-and NH2- anions in various distorted tetrahedral configurations, one by two B and two N atoms, another by four N atoms, and the third by one B and three N atoms. The Li configuration around B is nearly tetrahedral, while that around N resembles a distorted saddlelike configuration, similar to those in LiBH4 and LiNH2, respectively.