X-irradiation of single crystals of (C₆H₅)₂POH yields the (C₆H₅)₂PO radical, the phosphorus analogue of diphenyl nitroxide. The principal values of the ³¹P hyperfine coupling constants are 1439 MHz, 929 MHz and 908 MHz, which may be resolved into an isotropic component of 1092 MHz, and anisotropic components of 347 MHz, -163 MHz and -184 MHz. This implies that unlike diphenyl nitroxide, this radical is nonplanar (s/p ratio = 0·18, s-character = 0·11, p-character = 0·60).