Background: Both morbidity and mortality resulting from Staphylococcus aureus endocarditis are known to be high, and the incidence of this disease seems to increase. The Statens Serum Institut, Copenhagen, Denmark, made it possible for us to analyze the clinical features of S aureus endocarditis in a nation-wide population of non-drug addicts. Methods: Almost all Danish cases of bacteremia due to S aureus are reported to the Staphylococcus laboratory, Statens Serum Institut. The medical records were reviewed in cases reported from 1982 to 1991 in which the diagnosis of endocarditis was reported or suspected. Results: A total of 260 patients, 145 males and 115 females, fulfilled the diagnostic criteria. The median age was 67.5 years. In 83 patients, the diagnosis of endocarditis was not suspected clinically. The overall mortality rate among those patients whose disease was diagnosed clinically was 46%. Among the subset of patients who received medical therapy only and appropriate antistaphylococcal treatment, mortality was significantly associated with late congestive heart failure, age, and involvement of the central nervous system. Conclusions: A raised awareness of the paucity of clinical findings and a more frequent use of echocardiography as a screening method seem essential to improve the prognosis of patients with S aureus endocarditis. Involvement of the central nervous system constitutes a relative indication of early valve replacement.