The (C₆D₅)₃¹³C radical is produced by the X-irradiation of a single crystal of (C₆D₅)₃¹³C-H. The principal values of the hyperfine coupling with the ¹³C in the methyl position are determined as T₁ = 168 MHz, T₂ = 24 MHz, T₃ = 19 MHz. The corresponding spin density is compared with the values obtained in solution by earlier authors. The principal directions are consistent with crystalline structure and show that only one of the two molecules forming the asymmetric unit is broken during irradiation.