A radiotracer study has been made of self-diffusion in the rotator crystalline phase of 2,2′,3,3′-tetramethylbutane. Self-diffusion at temperatures Dt/m2 s–1= 2.2 exp –[85.7/RT]. At temperatures Eabt= 0.52±0.02 at temperatures < 353 K. This figure, which is greater than that recently measured for cyclohexane, is interpretable in terms of a slightly disordered lattice vacancy. At higher temperatures, Eabt < 0.52 which confirms that there is an increasing disorder in the lattice as the melting point is approached. The tracer diffusion coefficients are in excellent agreement with values obtained from n.m.r. line-narrowing studies on the same material. This agreement is presumed to be a consequence of the relatively ordered nature of the point defect.