Coagulase-negative staphylococci have long been regarded as apathogenic but their important role as pathogens and their increasing incidence have been recognized and studied in recent years. Although specific virulence factors are not as clearly established as they are in Staphylococcus aureus, it seems clear that factors such as bacterial polysaccharide components are involved in attachment and/or persistence of bacteria on foreign materials. Coagulase-negative staphylococci are by far the most common cause of bacteremia related to indwelling devices. Most of these infections are hospital-acquired, and studies over the past several years suggest that they are often caused by strains that are transmitted among hospitalized patients. Other important infections due to coagulase-negative staphylococci include central nervous system shunt infections, native or prosthetic valve endocarditis, urinary tract infections, and endophthalmitis. Intravenous treatment of systemic infections is usually required because coagulase-negative staphylococci have become increasingly resistant to multiple antibiotics.