Nosocomial endocarditis occurred in 22 patients who were discharged from a university hospital, a veterans' hospital, and a community hospital during the period of January 1976 to December 1985. Nosocomial episodes were 14.3% of the total endocarditis cases seen. Fourteen (63.6%) of 22 nosocomial endocarditis episodes occurred in patients over the age of 60 years, compared with 39 (29.5%) of 132 episodes of community-acquired endocarditis during the same period. Nosocomial endocarditis was due predominantly to Staphylococcus aureus or coagulase-negative staphylococci (77.4%) and, less often, to streptococci (13.6%). Intravascular devices were the source of bacteremia in ten (45.5%) of the nosocomial endocarditis episodes. The overall mortality rate was 40.9%, 50% in patients over the age of 60 years. Improved care of intravascular devices or prophylaxis before procedures could probably have prevented endocarditis in 12 of the 22 patients.