Coupled-cluster (CCSD) and density functional computations are used to investigate historically competing mechanisms for the permanganate oxidation of sulfides and sulfoxides. The calculations all lead to a mechanism of 1,3-dipolar cycloaddition of permanganate, as opposed to historical mechanisms of attack of the sulfur atom by one O or by Mn. Such a mechanism, reminiscent of ozonolysis, may prevail in most permanganate oxidations. The ab initio activation enthalpies are in reasonable agreement with the experimental data; the ab initio activation entropies are not, possibly because of problems with Eyring equation assumptions.