Infective endocarditis (IE) continues to be one of the most serious complications following cardiovascular surgery, particularly that for replacement of valves. In order to define more clearly the clinical course and the role of surgical therapy, clinical and necropsy data were reviewed in 16 adult patients with prosthetic aortic valvular endocarditis (PAVE) and compared with the experience cited in the literature. Positive blood cultures were obtained in each of the patients with bacterial endocarditis. Gram positive bacteria predominate and the onset of infection is usually later than 25 days postoperatively. In 11 of 16 patients, aortic insufficiency was recognized. Autopsy material demonstrated large perivalvular abscesses which loosened the attachment of the prosthetic valve in each case and which made successful operation unlikely. Aortic insufficiency appears to be of prognostic importance, since patients who developed aortic insufficiency early in the course of PAVE died. Survivors included patients who made an excellent response to medical therapy and who either did not develop aortic insufficiency or developed aortic insufficiency either late in the course or even after cure of PAVE, Poor response to medical therapy and progressive aortic insufficiency even in the absence of left ventricular failure appear to be indications for prompt surgical replacement of the prosthetic aortic valve.