Adhesion to epithelial cells and flagella-mediated motility are critical virulence traits for many Gram-negative pathogens, including enterotoxigenic Escherichia coli (ETEC), a major cause of diarrhoea in travellers and children in developing countries. Many flagellated pathogens export putative adhesins belonging to the two-partner secretion (TPS) family. However, the actual function of these adhesins remains largely undefined. Here we demonstrate that EtpA, a TPS exoprotein adhesin of enterotoxigenic E. coli, mimics and interacts with highly conserved regions of flagellin, the major subunit of flagella, and that these interactions are critical for adherence and intestinal colonization. Although conserved regions of flagellin are mostly buried in the flagellar shaft, our results suggest that they are at least transiently exposed at the tips of flagella where they capture EtpA adhesin molecules for presentation to eukaryotic receptors. Similarity of EtpA to molecules encoded by other motile pathogens suggests a potential common pattern for bacterial adhesion, whereas participation of conserved regions of flagellin in adherence has implications for development of vaccines for Gram-negative pathogens.