A model for calculating the dissociative ionization cross sections of diatomic molecules is developed. The activated state for dissociative ionizations is modeled to occur via the ejection of a bound electron and an excitation of another bound electron. This process is described by successive two-electron scatterings in the first Born and the binary-encounter approximations. Comparison of calculated cross sections with available experimental data for five diatomic molecules (H2, CO, N2, NO, and O2) shows good agreement with incident-electron energies above 200 eV. © 1975 The American Physical Society.