The electronic structure aspects of the M (S-1,3 P) + N2O(X(1)Sigma(+)) (M = Be, Mg, Ca) reactions are investigated using the CASSCF/MRMP2 (complete active space SCF and the multireference Moller-Plesset perturbation theory of the second order) computational methodology. The lowest adiabatic 1 (1)A(') and 1 3A(') potential energy surfaces (PESs) favor the bending dissociation mechanism of N2O in all studied cases. The rate-limiting channels are determined by the classical barriers that decrease in the series Be (8.9) > Mg (7.0) > Ca (1.2) kcal/mol, whereas the spin-forbidden reaction channels are found to be less important. A comparison with elaborated kinetic results (Plane et al. J. Phys. Chem. 1990, 94, 5255; Gas-Phase Metal Reactions; Elsevier: Amsterdam, 1992; Vinckier et al. J. Phys. Chem. A 1999, 103, 5328) on the Ca (S-1) + N2O(X(1)Sigma(+)) reaction is presented, and the differences in the kinetic behavior of the title reactions are discussed. Our results also indicate that the techniques based on the multiconfigurational wave functions are unavoidable if a correct topology of the PESs governing these reactions is needed.