Polarity is a characteristic of particular epithelial cells mediated by several protein complexes. The Scrib/Dlg/Lgl-polarity module represents one of the complexes regulating polarity. We hypothesized that Scrib is also present in endothelial cells to control directed processes involved in angiogenesis. mRNA and protein expression of Scrib was detected in human umbilical vein endothelial cells at a similar level as in different epithelial cell lines. Scrib RNAi blocked directed migration in chemotaxis and transwell assays, whereas random migration in the scratched wound assay was not affected. This effect was accompanied by an increased number and a disturbed orientation of cellular lamellopodia shown by Rac-1 staining. Furthermore, Scrib RNAi reduced endothelial sprouting in the spheroid assay but increased tube formation in the Matrigel assay. In a compensation assay, Scrib-downregulation favoured stalk cell rather than tip cell formation. Western blot and FACS analysis showed that Scrib RNAi reduced protein amount and surface expression of Integrin a5. Additionally, binding of a FITC-labelled RGD-peptide was reduced in cells missing Scrib. Furthermore, directed cell migration was only inhibited on Fibronectin but not collagen, suggesting a specific role of Scrib in integrin a5 signalling. In fliGFP zebrafish mutants, Scrib morphants showed a delayed sprouting of the intersegmental vessels and the transient formation of arterial-venous shunts in the caudal circulation demonstrating a delayed angiogenic development of the fish. In conclusion, Scrib represents a new endothelial protein mediating the translation of chemokine gradients into directed migration and is therefore required for sprouting angiogenesis in vitro and in vivo.