Experiments in both vertebrates and invertebrates have illustrated the competitive nature of growth and led to the idea that competition is a mechanism of regulating organ and tissue size. We have assessed competitive interactions between cells in a developing organ and examined their effect on its final size. We show that local expression of the Drosophila growth regulator dMyc, a homolog of the c-myc protooncogene, induces cell competition and leads to the death of nearby wild-type cells in developing wings. We demonstrate that cell competition is executed via induction of the proapoptotic gene hid and that both competition and hid function are required for the wing to reach an appropriate size when dMyc is expressed. Moreover, we provide evidence that reproducible wing size during normal development requires apoptosis. Modulating dmyc levels to create cell competition and hid-dependent cell death may be a mechanism used during normal development to control organ size.