The primary cilium, an antenna-like subcellular structure ('organelle') protruding from the outside of many types of vertebrate cells, has an important but previously overlooked role in guiding the growth of lymphatic vessels, shows a new study. The authors show for the first time that mouse and human lymphatic endothelial cells (LECs), which make up the inner and outer lining of lymphatic vessels, use primary cilia. They find that LEC primary cilia may direct the growth of a functional lymphatic network, not only during prenatal development, but also throughout life during inflammation and wound healing and in response to cancer. They show that mice in which the formation of primary cilia in LECs is prevented develop lymphatic vessels that are locally overgrown, suggesting that signals received by primary cilia may guide proper lymphatic vessel growth patterns. These results, published today in the open access journal Frontiers in Cell and Developmental Biology, have implications for human medicine.