Contamination of contact lenses is thought to increase the risk of infectious keratins, yet factors promoting attachment of bacteria to contact lenses are not fully understood. It has been suggested that strains ofPseudomonas aeruginosaattach to mucosal surfaces via pili which are appendages found on some strains. This study investigated the role of pili and the effect of incubation time on the attachment ofP. aeruginosato 20 unworn hydrogel lenses representative of each of the four FDA categories. Ten lenses were incubated for 15 minutes and another ten for 180 minutes. Lenses were incubated with either PAK+P. aeruginosawhich possessed pili or its isogenic mutant pair, PAK-, which was genetically similar except for the absence of pili. Bacteria were quantified, following homogenization of the contact lens, by viable counts. Non-piliated bacteria were significantly more likely to adhere to the lenses (p<0.001). A significant interaction between lens type and incubation time was observed (p<0.05); thus it is difficult to generalize about either of these effects in isolation. These results show that surface characteristics may confer an attachment advantage to bacteria.