There is considerable controversy regarding antimicrobial prophylaxis against infective endocarditis for routine sigmoidoscopy without biopsy in patients with underlying valvular heart disease. Sigmoidoscopy is known to produce brief, low-grade bacteremia in some patients. Persons with mitral valve prolapse (MVP) may be at risk of infective endocarditis developing during transient bacteremia. We describe a 67-year-old man with known MVP in whom enterococcal endocarditis developed following routine sigmoidoscopy. We believe this to be the first such reported case.