Infectious endocarditis involving intracardiac prosthesis continues to be a common and dangerous complication of cardiac surgery, but the incidence and severity of the disease are probably underestimated in this country. 14 cases of prosthetic endocarditis observed in a 5 years period are reported in this paper. 7 were early cases and 7 late cases. Etiology, clinical course, and pathological lesions, were similar in the two groups, while mortality was higher in the first group (100%) than in the second (85%). Delay in the diagnosis, negative blood cultures in a third of all cases, and doubts in indications for surgery, were the main reasons for a higher mortality than usual. Only one patient was reoperated on, unsuccessfully, but no patient who had not improved after two weeks of correct antibiotic treatment, survived; such cases, especially if diagnosis has been late and/or blood cultures negative, should be reoperated on without delay. The greatest efforts should be made in the prevention of the disease and, in particular, pre-operative and late post-operative prophylaxis should become more rigid and systematic.