A Monte Carlo exchange technique is used to study segregation in thin ceramic films with application to the Mg1-xMnxO{100} and {210} surfaces. Unlike previous atomistic simulations of segregation the method is not restricted to the dilute limit. For all compositions studied (0 <= x <= 1), the surface is Mn2+ rich; the occupancy of sites by Mn2+ decreases rapidly with depth. The ratio of the number of Mn2+ to Mg2+ ions at the surface decreases as a function of temperature. Segregation is greater at {210} than {001} surface, consistent with the relative difference in surface energies. Surface concentrations as a function of temperature and film composition are determined directly from the simulations. The calculated enthalpies of segregation are strongly dependent on the surface coverage, particularly for low Mn2+ mole fractions. (c) 2006 Elsevier B.V. All rights reserved.