The chloromethane cation and dication have been studied using the complete active space self-consistent field method followed by a multireference perturbative configuration interaction. The (2)E ground state of CH3Cl+ presents a weak Jahn-Teller distortion, the (2)A’ and (2)A " components being separated by only 3.4 kcal/mol with very similar geometries. Both states are equilibrium structures. Contrary to previous calculations, the lowest singlet and triplet states of CH3Cl++ are calculated to be stable. While the (3)A(2) State keeps the neutral C-3 upsilon symmetry the (1)E singlet state shows a large Jahn-Teller effect, with a splitting of 32.7 kcal/mol in favor of the (1)A’ state, which is the ground state of the molecule. The planar (1)A’ state of CH2ClH++ is found to be the most stable isomer, lying 41.4 kcal/mol below the corresponding state of CH3Cl++. The (3)A " state, which lies 22.59 kcal/mol above the (1)A’ state, has a nonplanar C-s-symmetry geometry. Finally, the CH3Cl++ ((1)A’) --> CH2ClH++ ((1)A’) isomerization takes place via a C-1-symmetry geometry. Finally, the CH3Cl++ ((1)A’) --> CHClH++ ((1)A’) isomerization takes place via a C-1-symmetry transition state, with an energy barrier of 32.85 kcal/mol.