Patients undergoing continuous ambulatory peritoneal dialysis (CAPD) are at an increased risk of peritonitis following colonoscopy with or without polypectomy. Guidelines for peritoneal dialysis patients recommend administration of prophylactic antibiotics and drainage of the abdomen before colonoscopy. In this report, we describe a 53-year-old woman on CAPD who underwent colonoscopy with polypectomy and developed peritonitis within 24 hours. She presented with severe abdominal pain, typical rebounding tenderness, and turbid dialysate containing increased white blood cells with a predominance of neutrophils. A culture of the patient's peritoneal fluid grew polymicrobial species including Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis. She was treated with intraperitoneal and intravenous administration of combination antibiotics, and she fully recovered within 3 weeks. We suggest that nephrologists and endoscopists should be familiar with the risks and follow the guidelines to prevent such complications in CAPD patients. If peritonitis occurs, medical therapy with antibiotics should be considered before surgical intervention for catheter salvage.