Ion photodesorption processes from carbon monoxide condensed in multilayers have been studied for photon energies between 12 and 60 eV. In the low energy range (12-25 eV), only the CO+ ion desorbs and the desorption is induced by the formation of excited neutral states. In the high energy range (25-60 eV), a large variety ed ions desorb : C+, O+, CO+, C2O+, (CO)(2)(+), C3O2+, and C3O+. The desorption threshold for these ions is around 30 eV and is assigned to the formation of satellite states. The ion desorption is related to fragmentation processes and ion-molecule reactions on the surface. Comparison with gas phase results show that the dissociative ionization of CO can be modified in the condensed phase by charge-transfer processes. Kinetic energy measurements of the desorbed ions support the proposed mechanisms.