We describe a case of Hemophilus parainfluenzae endocarditis in a previously healthy 26-year-old man, and review 21 cases from the literature. Although H parainfluenzae is considered to be part of the normal flora of the upper respiratory tract in man, it can cause serious disease. H parainfluenzae endocarditis is often difficult to diagnose. The patients generally had a history of recent infection of the upper respiratory tract, but a majority denied previous heart disease. Upon entry to the hospital, after an average of seven weeks of febrile illness, nearly one third of patients were found not to have a heart murmur. Furthermore, the organism was often difficult to grow from blood cultures, a problem possibly related to the need for accessory growth factors. The mortality with modern therapy was 12%, and the major complication was cerebral embolus. Antibiotic therapy of choice is ampicillin, generally used together with an aminoglycoside, though ampicillin alone may be sufficient.