Solid Perfluoromethlycyclohexane has been studied by X-ray diffraction, n.m.r., and e.s.r. The two former methods confirm the existence of several thermodynamically stable crystalline phases between 77 °k and the melting point (234 °K): phase I (227 < T < 234 °K), phase II (173 < T < 227 °K), phased III (T < 173 °K) and that of a metastable phase (II′) below 130 °K. When the temperature is raised, the n.m.r., indicates successively the rotation of CF3(phases II′ and III), the reorientation (phase I). Similar information is obtained from e.s.r. concerning the motions ofradicals trapped in PFMCH.The comparison betweenganisotropy, measured from the position of the peaks of e.s.r. spectra and that deduced from their second moments suggests a wide distribution of reorientaion correlation times for radicals in the metastable phase.