The crystal structure of tetrameric phosphonitrilic isothiocyanate, N4P4(NCS)8, has been determined by three-dimensional X-ray studies from data collected on a Picker FACS-1 automated diffractometer. The compound crystallizes in the triclinic space groupwitha = 8.098(8),b = 8.018(7), c = 9.937(10) Å, α = 104.08(7), β = 99.42(7), γ = 95.42(7)°, and one molecule per unit cell. The structure was solved from 1766 independent non-zero reflections and refined to a conventionalRfactor of 0.063. Nitrogen atoms of two isothiocyanate groups are bonded to each phosphorus atom of the eight-membered phosphorus–nitrogen ring. The ring has a chair configuration. The average dimensions of the structure are P—Nring = 1.543 + 0.017, P—Nisothiocyanate = 1.644 ± 0.011, N—C = 1.168 ± 0.008, C—S = 1.535 + 0.009 Å,and NĈS = 176.6 ± 1.1°