The precise nature of the excited states of Mn-2(CO)(10) leading to the well-known photochemistry-both Mn-Mn and Mn-CO bond breaking upon low-energy excitation-is still unclear. In order to identify possibly dissociative excited states (either Mn-Mn, Mn-COax or Mn-COeq), the nature of the highest occupied Mn-Sd orbitals is analyzed as well as the composition of the virtual orbitals. The following features are noted. (a) The low-energy excitations at 337-355 nm arise from sigma --> sigma* and d pi --> sigma* excitations, while d --> d excitations occur at much higher energy. (b) The Mn-Mn sigma bonding HOMO as well as the sigma* LUMO cannot simply be classified as arising from the 3d(z2) components of e(g) parentage in the local octahedrons around Mn, they have little 3d(z2) - 3d(z2) (anti)bonding character but significant contributions come from Mn-4p(z) and CO-2 pi(eq) orbitals. Mn-Mn sigma antibonding is only strong in the sigma* orbital due to these contributions. (c) Due to the strong involvement of Mn-4p(z), th 3d(z2) orbital not only occurs in the sigma and sigma* orbitals but also in a higher set of virtuals, denoted sigma,’sigma’*, similar to 1.5 eV above the sigma* orbital. Antibonding with axial CO’s is strong in these higher virtuals but absent or weak in the sigma and sigma* orbitals. sigma antibonding with equatorial CO’s is strong in the 3d(x2)-y(2) orbital of e(g) parentage, that is located very high in the virtual spectrum, similar to 2 eV above the sigma* orbital. Mn-Mn dissociation will occur only from the sigma --> sigma* excitation; CO loss will probably occur from the high-lying d --> d excited states (excitations into sigma’,sigma* and the 3d(x2-y2)). The observed photochemistry at low energy Will have to be explained from curve crossings between the low-energy excited states and the photoactive states.