Staphylococcus aureus and Staphylococcus epidermidis are frequently associated with medical device infections that involving biofilm formation on the device surface. Biofilm formation and host colonisation have been linked to staphylococcal surface proteins Aap, SasG and Pls. These surface proteins are members of the Periscope Protein class, comprising a repetitive region (“B region”) and an N-terminal host colonisation region ("A region") [1]. The host colonisation region has been predicted to incorporate a lectin-homology fold, typically associated with glycan binding. We previously showed that repetitive regions comprised of E-G5-domains (as found in Aap, SasG and Pls) can form highly elongated structures [2]. In the context of a Periscope Protein, length variation of the central repetitive region has been predicted to result in projection of the host colonisation domain at variable distances from the bacterial cell surface. We have determined the structures of the host colonisation lectin domains of SasG, Aap and Pls and a lower resolution structure of the Aap lectin domain with contiguous E-G5 repeats. The proximity of the N- and C-termini of the lectin domains suggests that the adhesin fold will be positioned at the cell distal tip of the variable length rod. Previously, proteolytic cleavage or a deletion within the A-region have been shown to induce biofilm formation. The structures we have determined here infer a potential link between these observations. Interestingly, like the canonical lectin fold, the Aap, SasG and Pls A domains bind a metal ion, but feature one key difference that indicates a non-canonical ligand binding mechanism may underpin bacterial adhesion to the host.