Electron propagator calculations on the lowest 14 vertical ionization energies of the para, meta, and ortho isomers of dichlorobenzene are performed using the OVGF and P3 approximations, where Feynman-Dyson amplitudes are equivalent to canonical molecular orbitals. Cl p orbitals destabilize the e(1g) set of benzene to produce the molecular orbitals associated with the two lowest ionization energies. Holes corresponding to four higher final states have mostly Cl 3p character. The remaining molecular orbitals strongly resemble their benzene counterparts, but significant Cl admixtures are present in most cases. Previous assignments for rn-dichlorobenzene are confirmed, and remaining uncertainties in the ortho and para spectra are resolved. Basis sets with up to 304 contracted functions are used. Agreement with experimental ionization energies is close.