['Appendiceal tumors represent a subset of colonic neoplasms that frequently defy early diagnosis only to present at advanced stage with peritoneal metastasis. Data on early detection by colonoscopy is limited to case reports or series. The aim of this study is to determine the diagnostic yield of colonoscopy in detecting appendiceal lesions in patients with appendiceal adenocarcinoma and pseudomyxoma peritonei.', 'We reviewed clinicopathologic data on 121 consecutive patients with histologically confirmed appendiceal adenocarcinoma with pseudomyxoma peritonei presenting to our institution for intraperitoneal hyperthermic chemotherapy (IPHC) and cytoreductive surgery between February, 1993 and August, 2007, focusing on the colonoscopy findings.', 'Preoperative colonoscopic data were available on 64 patients (average age = 51; 52 for IPHC patients). Abnormal findings included seven patients with appendiceal lesions (11%), 12 patients with cecal abnormalities (19%), and 28 patients with polyps (44%). Twenty-three patients (36%) had a normal colonoscopy. Malignancy was documented in two of the 64 (3.1%) patients on preoperative colonoscopy biopsies.'] Is adenocarcinoma of the appendix rarely detected by colonoscopy?