Capnocytophaga canimorsus, a bacterium rarely encountered by clinicians, was responsible for the development of peritonitis in an 18-year-old white male on automated peritoneal dialysis following the puncture of his dialysis tubing by a domestic cat. Although more than 100 cases of septicemia caused by C. canimorsus have been reported, this is the first report of the organism causing peritonitis in a patient receiving peritoneal dialysis. Of interest, the patient had a prior episode of peritonitis secondary to Pasteurella multocida, also following transmission from the same cat.