It is shown by x-ray diffraction, energy-dispersive x-ray spectrometry, and electron probe microanalysis that, at 800degreesC, the Ni-P system contains four phosphides in the composition range 25-33 at % P: Ni3P, Ni5P2, Ni12P5, and Ni2P. The structure of Ni5P2 is determined by single-crystal x-ray diffraction: sp. gr. P(3) over bar c1, new structure type, a = 0.6613(3) nm, c = 1.2311(6) nm, 347 independent hkl reflections with F-hkl > 4sigmaG(F-hkl), R-F = 0.0346. The key structural features of Ni5P2 are discussed.