In Drosophila imaginal wing discs that contain cells that proliferate at different rates because they carry Minute mutations,fast-growing, non-minute M+ cells contribute much more to the final disc than do slow-growing M/+ cells. Yet, the final disc size is unaffected. This suggests that specific interactions between cells may cause the elimination by apoptosis of slow-growing cells by fast-growing cells- so- called cell competition. However, Ginés Morata and colleagues now report that prevention of apoptosis does not affect the compartment size in developing imaginal discs, even in the presence of overgrowing M+ clones (see p. 3747). The overgrowth of M+ cells, they report, is solely due to their higher division rate. The researchers propose, therefore, that the contribution of each cell type to the disc compartment is exclusively determined by its division rate rather than by cell competition, and that a size control mechanism stops growth once the compartment reaches the correct size, a conclusion that is supported by their computer simulations.