An association between adherent biofilm production on tissue culture plates and expression of a specific polysaccharide intercellular adhesion (PIA), which is functionally involved in cell clustering, was investigated for 179 Staphylococcus epidermidis isolates. Of the S. epidermidis strains, 50.8% were biofilm producers (A570 of > 0.1). There was a significant positive association between biofilm production and PIA expression: 86.8% of biofilm-producing S. epidermidis strains produced PIA as detected with a specific coagglutination assay. In contrast, 88.6% of the biofilm-negative isolates did not express PIA (P < .001). A linear association between the amount of PIA produced as detected by inhibition ELISA and the amount of biofilm produced was established for 49 S. epidermidis strains, representing a continuum from biofilm-negative to strongly biofilm-producing (r = .81, P < .001). Apparently, PIA is important for biofilm accumulation in the majority of clinical S. epidermidis isolates.