Clinical and bacteriological information on Staphylococcus aureus endocarditis from hospitals all over Denmark in the period 1976-1981 was reviewed in 119 cases, 61 females and 58 males. Patient ages ranged from 16 days to 85 years, with a median age of 63 years. The overall mortality was 71%. The mortality correlated significantly with such factors as age, hospital-acquired infections and resistance to penicillin in infecting strains. Hospital-acquired infections occurred in 38% of the patients. The distribution of phage types among strains isolated from blood cultures from patients with endocarditis corresponded to that of strains from other septicaemia cases. Group I and group III strains and strains of the 94, 96 complex comprised 74% of the phage types of the present material. Infections of the skin were the most common portal of entry for the infecting strains. Apart from drug addicts, of which 11 cases were included, mortality did not correlate with the presence of any underlying diseases.