A 1-year-old boy was admitted to the hospital with Haemophilus influenzae meningitis. On the second hospital day a heart murmur heard on admission seemed louder. No signs of congestive heart failure were present. An echocardiogram demonstrated a persistent echo-dense mass behind the anterior leaflet of the mitral valve. A presumptive diagnosis of endocarditis was made. After ten days of antibiotic treatment the child was considerably improved. Treatment was continued for endocarditis. Over the next several days the infant's condition deteriorated. On the 16th hospital day he died. Autopsy examination showed a large vegetation attached to the posterior mitral valve leaflet. Bacterial endocarditis caused by H influenzae is uncommon at any age and rare in children. Echocardiography provided a definitive diagnosis early in the hospital course of this patient.