A 78-year-old woman developed fatal endocarditis of her prosthetic aortic valve, caused by Bacteroides fragilis fragilis, and associated with ovarian carcinoma. The strain showed multiple antibiotic resistance, including resistance to beta-lactam agents and combinations with beta-lactamase inhibitors. Seventeen previously described cases of endocarditis caused by Bacteroides spp. have been found in the literature. The mean age of the 18 patients was 50.3 years, the gastro-intestinal tract was the most common site of associated disease, embolism occured in ten cases and eight patients died. Previous isolates showed the antibiotic susceptibility customarily associated with the B. fragilis group.