AIMS: To analyse the characteristics of infective endocarditis (IE) in patients with diabetes mellitus (DM), and to evaluate the prognostic significance of DM according to insulin use. METHODS AND RESULTS: A total of 559 patients with definite IE including 75 patients (13%) with DM (insulin use n = 22; oral antidiabetic n = 53) were evaluated. Comparison of insulin-DM, oral-DM, and non-DM patients showed an older age (66 +/- 13, 66 +/- 10, 58 +/- 17, respectively; P = 0.004) in DM patients, and more frequent IE on prosthetic valves (32, 11, and 15%, respectively; P = 0.068) in insulin-DM patients. Oral streptococci (0, 8, and 18%, respectively; P = 0.016) were less frequently the causative organism than staphylococci (64, 26, and 29%, respectively; P = 0.002) in insulin-DM patients. Vegetations, dehiscence, abscess, and regurgitation rates did not differ among the three groups, nor did cardiac surgery rates (32, 47, and 48%, respectively; P = 0.334), but in-hospital mortality was higher in insulin-DM patients (50, 19, and 15%; P