BACKGROUND : Collagenous colitis (CC) is a clinicopathologic syndrome characterized by chronic watery diarrhea and distinctive histopathologic features. Spontaneous perforation of CC is extremely rare, because CC is usually managed medically, and the need for surgical intervention is rare. We report a surgical case of spontaneous colonic perforation of CC with acute abdomen disease. METHODS : A 77-year-old man was admitted to our hospital for abdominal pain and watery diarrhea. Computed tomography (CT) showed a thickened bowel wall with edema involving free air around the splenic flexure of the colon. Therefore, we performed emergency surgery with a diagnosis of colonic perforation. Intraoperative findings revealed colonic necrosis at the splenic flexure, so we performed a left hemicolectomy. Histopathological examination revealed typical findings of CC, a thick subepithelial collagenous band and deep ulcers with perforation. The postoperative course was uneventful, and the patient was discharged on the 28th postoperative day. After changing the proton pump inhibitor (PPI) from lansoprazole (LPZ) to rabeprazole (RPZ), he has not complained of diarrhea symptoms. CONCLUSIONS : Although spontaneous perforation is a rare complication of CC, it is possible to be diagnosed by symptom of acute abdomen disease. This is the seventh case of spontaneous colonic perforation of CC worldwide.