A 33-year-old, active intravenous drug-abusing male infected with the human immunodeficiency virus developed endocarditis due to Arcanobacterium haemolyticum. Empirical treatment with ampicillin plus gentamicin failed to achieve a marked clinical improvement. When the results of antibiotic susceptibility were available (ampicillin MIC < or = 0.06 mg/l; ampicillin MBC 2 mg/l; MBC:MIC ratio > 32) therapy was changed to vancomycin plus gentamicin. During the following days progressive clinical and radiological improvement was observed. The patient received antibiotics for 30 days and no relapse occurred during a 14-month follow-up. The literature of endocarditis due to this uncommon bacterium is reviewed here.