The variation in the cathodoluminescence output of thin ZnS:Mn films as a function of beam voltage has been examined. The results have been analysed in terms of the generation, diffusion and recombination of charge carriers. Values obtained for the apparent diffusion lengths and reduced surface recombination velocities were of the order of 0.07 mu m and 25 (dimensionless) respectively. There were indications that the diffusion length depended on the film thickness and a possible reason for this is discussed.