Development of the vasculature is one of the earliest events during embryogenesis, preceding organ formation. Organogenesis requires a complex set of paracrine signals between the vasculature and the developing nonvascular tissues to support differentiation and organ growth. However, the role of endothelium in controlling organ growth and, ultimately, size is little-understood. In this review, we summarize new data regarding the endothelium function in order to provide a more comprehensive understanding of the communication between the endothelium and the organ's tissue.