A study of the magnetic behavior of Pr 2 NiO 4 single crystals is presented. Single-crystal neutron diffraction, magnetic susceptibility, and isothermal magnetization at various temperatures and magnetic fields applied along the different crystallographic axes are used to obtain an overall picture of the magnetic behavior. The metamagnetic transition is studied for temperatures below the structural phase transition (T C1 ≃117 K). Between 1.5 K and T C1 the dependence of the spin arrangement with magnetic field is presented, and an H-T phase diagram is proposed. Above T C1 and up to the Neel temperature (T N ≃325 K) the system behaves as an antiferromagnet with the magnetic moments along the x direction