We report two cases of Campylobacter fetus endocarditis. The first case involved a bicuspid native aortic valve in a 60-year-old woman, and the second involved a prosthetic aortic valve in a 76-year-old woman. No source of infection was identified in either case. Despite antibiotic therapy, hemodynamic deterioration necessitated valve replacement; both patients recovered completely. C. fetus is an uncommon cause of human infection but may be responsible for severe illnesses such as endocarditis and thrombophlebitis because of its tendency to attack the vascular endothelium. Review of the literature revealed 21 cases of endocarditis caused by this organism, usually involving the aortic valve. To our knowledge, there are only two reported cases of prosthetic valve endocarditis. Our second patient is the oldest one encountered so far with this condition.