The risk of bacterial endocarditis in infants with bacterial sepsis was assessed by review of clinical and autopsy records (1930 to 1972). There were 12 cases of bacterial endocarditis among 847 patients (1.4%) dying with bacterial sepsis; a single survivor was noted during the entire period. Of the 12 autopsy patients, six had underlying congenital heart disease (CHD). Among 61 patients with bacterial sepsis associated with CHD, six acquired bacterial endocarditis (10%), whereas in 786 infants with sepsis but without underlying heart disease, only six developed bacterial endocarditis (0.8%) (P <.01). There is a high mortality in infants with bacterial endocarditis, and an increased risk of it in infants with sepsis and CHD.