The transmembrane protein Crumbs is essential for establishing epithelial apicobasal polarity but, puzzlingly, this function appears to be largely dispensable in developing Drosophila imaginal discs – epithelia that make adult organs during metamorphosis. On p. 641, Emily Richardson and Franck Pichaud now identify a surprising new role for Crumbs in regulating Drosophila organ size. Using mutant and RNA interference analysis, the researchers found that crumbs function is dispensable for head formation, but regulates head, eye and wing size, and that loss-of-function mutant tissues overgrow because of increased cell proliferation. The researchers further report that eye overgrowth depends on Notch signalling, with a loss of crumbs function leading to an increase in the endocytosis of Notch and its ligand Delta, an event required for Notch downstream activity. Based on these and other data, the researchers conclude that Crumbs can limit ligand-dependent Notch activation and that Crumbs and endocytic mechanisms are jointly involved in organ size control, a finding that should stimulate future research in the field.