To define the clinical, microbiological, and therapeutic characteristics of haemophilus endocarditis, we reviewed the charts of 42 adults with haemophilus endocarditis (native valve disease, 37; prosthetic valve disease, five) who were followed up between 1983 and 1995 in France. The mean duration of symptoms before diagnosis was 34 days. The causative Haemophilus species were as follows: H. parainfluenzae (26 adults), H. aphrophilus (9), H. paraphrophilus (4), and H. influenzae (3). According to the Duke criteria, 38 cases of endocarditis were definitive and four were possible. Thirty-nine patients received combination antibacterial therapy and three received therapy with a beta-lactam agent alone (mean duration, 46 days). Arterial embolism occurred in 15 patients. Cardiac surgery was indicated for 18 patients; 16 of these surgeries were performed within 3 months. Two patients died of heart failure. In conclusion, haemophilus endocarditis is rare and is mainly due to H. parainfluenzae. Although surgery is often necessary, haemophilus endocarditis has a favorable prognosis.