Nickel chromite is a normal spinel whose structure has atetragonal distortion below about 310°K. The structure parametershave been determined by neutron diffraction at 77°K, at whichtemperature thec/aratio of a face-centered unit cell is 1.04. Thespace group isI41/amdwith four Ni ions in positions 4(a), eightCr ions in positions 8(d), and 16 O ions in positions 16(h) withy = 0.239andz = 0.392. The two independent Cr-O distances are1.98 A and 1.99 A, indicating that the octahedron is not greatlydistorted. The tetrahedron around the nickel is elongated bynearly 14% parallel to thecaxis. Below a Curie temperature ofabout 65°K, nickel chromite has a small ferromagnetic moment.The neutron diffraction pattern at 4.2°K shows extra peaks whichcan be indexed on the basis of a primitive cell having the samedimensions as the body-centered chemical cell. The intensities ofthese peaks cannot be accounted for by any simple model for themagnetic structure. In fact, a systematic search of possiblestructures belonging to magnetic space groups with symmetriesas low as classesm′m′2 andmm′2′ has failed to turn up anystructure which is consistent with the diffraction data.