The purpose of this retrospective study of 28 cases of staphylococcal endocarditis on cardiac valve prosthesis was to evaluate the prognosis of that disease and the possible causes of its recent improvement. Between March 1977 and May 1987, 69 patients were treated for bacterial endocarditis on cardiac valve prosthesis. Among these, 28 patients (19 men, 9 women, mean age 53.2 +/- 14.3 years) had staphylococcal endocarditis (Staph. epidermidis in 18 cases, Staph. aureus in 10 cases) of early (10 cases) or late (18 cases) onset. Complications were present in no less than 27 out of 28 patients, the most frequent being heart failure, embolism or neurological disorders. The mortality rate was high (61 p. 100). Among the clinical variables studied, only a state of shock seemed to be predictive of death. Mortality was higher in the group treated medically (100 p. 100) than in the group treated surgically (50 p. 100). Since 1984, however, a significant decrease of mortality was noted; it coincided with the systematic use of vancomycin but also with surgical treatment in all cases. As a result of this study, we suggest that all patients with staphylococcal endocarditis on cardiac valve prosthesis should be operated upon and that this should be done as soon as possible, before the end of the classical antibiotic therapy period.