The influence of the environment near the radical site on the stereoselectivity of the homolytic substitution reaction of variously substituted cyclohexyl radicals on the peroxidic oxygen of a peroxy acid has been studied using the thermal decarboxylation of peroxy acids. This reaction leads to stereoisomeric alcohols[Formula: see text]The radical behaves as if it were planar and, in general, an axial approach of the reagent is strongly favoured except when substituents increase the steric hindrance of the radical.The stereoselectivity is explained in terms of the relative importance of steric effects (for the axial approach) and of bond interactions (for the equatorial approach). It also depends on the flexibility of the ring. [Journal translation]