A cubic Rh⁺ centre in NaCl is studied with electron paramagnetic resonance (EPR) at Q-band (34 GHz). Its ΔM_S = 1 EPR spectrum is shown to be broadened due to random distortions, lowering the cubic symmetry. At high microwave power, a sharp double quantum transition is observed, which exhibits a partially resolved hyperfine structure. From the formation conditions of this paramagnetic centre in solution and melt-grown NaCl crystals, its Rh²⁺ precursor centres are determined.