Patients admitted to the ICU have a higher risk of nosocomial infection than other hospitalized patients. Whereas general medical/surgical ward patients have a 6% overall risk of acquiring an infection during their hospital stay, critically ill patients in the ICU have an 18% risk (P greater than 0.001). During this 2-year study, 440 of 2441 patients admitted to an ICU developed nosocomial infections. Patients who had prolonged ICU stays and those on the obstetrics and gynecology, orthopedics, and general surgery services were more likely to become infected. The most common bloodstream pathogens were Staphylococcus epidemidis, Staphylococcus aureus, and Serratia and Pseudomonas species.