Ab initio techniques at the ump2/6-31G*//ump2/6-31G* level has been used to study the conversion of cyclopropane radical cation to propene radical cation. This process has been found to be have an asynchronous one-step mechanism with an activation energy of about 30 kcal/mol. The ground state of the reactant has a C-2v symmetry With a (2)A(1) electronic state. The global minimum is the C-s propene radical cation. No stable intermediates of the trimethylene radical cation type have been encountered.