Phlegmonous proctitis is a rare condition; it was first described in 1940. We report the case of an elderly woman who presented with acute severe lower abdominal pain, tenesmus, and fever. A computed tomography of the whole abdomen revealed a long segment of circumferential wall thickening of the rectum and rectosigmoid colon. Colonoscopy was done subsequently and showed marked edematous and erythematous rectal mucosa. When rectal tissue biopsy was performed, a large amount of pus came out at the biopsy site, which led to the diagnosis of phlegmonous proctitis.
Keywords: Biopsy; Colonoscopy; Phlegmonous proctitis; Rectosigmoid colon; Rectum.