Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the pre dominant cause of implanted medical-device related infections. The formation of adherent multilayered biofilms embedded into a glycocalyx composed of exopolysaccharides on implanted devices is believed to be essential for the pathogenesis of S. epidermidis infections. Biofilm formation may be separated into primary attachment of bacteria to native or modified polymer surfaces followed by proliferation of attached bacterial cells leading to accumulation of multi-layered cell-clusters and glycocalyx formation. Recent progress in the understanding of the molecular mechanisms cooperating in S. epidermidis biofilm formation is reviewed and current thinking on the relevance of these mechanisms for S. epidermidis device-related infections is discussed. (C) 1999 The Hospital Infection Society.