The prognostic factors of 122 patients suffering from prosthetic valve endocarditis between 1978 and 1992 were studied by univariate and multivariate analysis. The principal causative organisms were Staphylococcus aureus (33%), streptococci (20%), coagular-negative staphylococci (12%), enterococci (10%) and gram-negative bacilli (9%). The 4 month survival rate was 66% (42 deaths). The main predictive factor for death was infection with S. aureus (75% vs 15% with other organisms). In S. aureus infection, multivariate analysis identified the following predictive factors for death: a prothrombin ratio less than 30% (RR = 8.3), mediastinitis (RR = 4.9), cardiac failure (RR = 4.4) and septic shock (RR = 2.6). In cases of infection with other organisms, the following factors were predictive of death: a prothrombin ratio of less than 30% (RR = 32.26), renal failure (RR = 7.31) and cardiac failure (RR = 6.07). In patients with S. aureus infection, survival was better after than without surgery: 9/20 (45%) versus 0/20 (p < 0.001). In infection with other organisms, there was no difference in a survival after surgical (89%) or medical therapy (81%). Chronic endocarditis relapses over 1 to 5 years was observed in 9 cases. All patients were reoperated a total number of 18 times with 5 deaths. Very prolonged antibiotic therapy is recommended in these patients. The authors conclude that endocarditis not due to S. aureus and without complications may be treated medically. Rapid reoperation is necessary in all other cases.