Colonoscopy is a relatively safe procedure with few complications. However, it may be accompanied with complications such as bleeding, perforation and, rarely, acute appendicitis. Acute appendicitis occurs when the appendiceal opening is obstructed by lymphoid hyperplasia, fecalith or foreign materials. In case of late detection, acute appendicitis can results in perforation and panperitonitis. Therefore early diagnosis and proper management is mandoctory. We experienced a 70-year-old female patient who visited for abdominal pain and tenderness after the diagnostic colonoscopy and was found to develop acute appendicitis. Herein, we report the case with the review of literatures. (Korean J Gastrointest Endosc 2005;31:189192)