From 1975 to 1989, 307 consecutive episodes of infective endocarditis were diagnosed in our hospital. Of those, 35 were cases of late prosthetic valve endocarditis, defined as those occurring after 12 months of valvular replacement. Blood cultures grew streptococci in 15 patients (43 percent), staphylococci in seven (20 percent), enterococci in five (14 percent), Gram-negative bacilli of HACEK group in four (11.5 percent), and Candida in one. Blood cultures were negative in three cases (prosthetic infection was confirmed at surgery). Heart failure due to prosthetic dysfunction occurred in seven patients (20 percent) and emboli in 12 (34 percent). Early valvular replacement was performed in six patients (17 percent). Complications and mortality were dependent on the infective agent. Overall mortality was 23 percent, no death occurred from streptococcal infection, whereas mortality with endocarditis by organisms of the HACEK group and Staphylococcus was 50 percent and 43 percent, respectively. During a mean follow-up of five years, 11 patients (those with prosthetic leaks diagnosed during the active infection and patients with biologic prostheses) required surgery. There was one relapse in a patient with staphylococcal endocarditis and one recurrence, six years after the initial episode. We conclude that immediate prognosis of late prosthetic valve endocarditis depends on the infective agent. Although the immediate prognosis of streptococcal infections is good, the need for early reoperation during follow-up due to progressive perivalvular leak is high. Also, it appears that deterioration of bioprostheses proceeds swiftly after the cure of infection.