X irradiation of a single crystal of boron trichloride at 77 K yields at least two different radicals. A brief exposure to UV irradiation, however, leaves only one radical whose ESR spectrum shows hyperfine coupling from one boron (¹⁰B, ¹¹B) and two equivalent chlorine (³⁵Cl, ³⁷Cl) nuclei and which is identified as BCl₂. The g tensor, ¹¹B magnetic hyperfine tensor,³⁵Cl magnetic and quadrupole hyperfine tensors have been determined and analyzed in terms of the radical's electronic structure. Problems arising in relating the principal direction of the various tensors to the molecular geometry are discussed. BCl₂, is nonlinear with a ClBCl angle of approximately 122° and with the unpaired electron mainly localized on the boron atom.