BACKGROUND Although diverticular disease is well described and treated in daily clinical practice, there are cases that attract great interest because of their complexity and difficulty in management. Herein, we describe a rare case of colo-colonic fistula-complicated diverticulitis that necessitated urgent surgical intervention. CASE REPORT A 76-year-old female patient with a known history of diverticular disease of the sigmoid colon presented in the Emergency Department for evaluation of left lower quadrant abdominal pain. The clinical and radiological examinations revealed a recurrent episode of acute diverticulitis of the sigmoid colon. However, it was of great interest that we detected a sigmoido-cecal fistula in the abdominal computed tomography (CT). The patient was admitted to the hospital for conservative treatment. After 48 hours, the patient's clinical status deteriorated, with pain aggravation, abdominal distension, bloating, and metallic bowel sounds. The simple abdominal x-ray revealed large-bowel obstruction and the CT demonstrated worsening inflammation of the sigmoid colon. An exploratory laparotomy revealed an inflamed dolichol-sigmoid colon forming a fistulous tract with the cecum and thus, mimicking a closed loop obstruction. The sigmoid colon was transected en bloc with the sigmoido-cecal fistula and a Hartmann's procedure was performed. CONCLUSIONS This case is extremely unusual as the patient presented at the same time two complications of diverticular disease, both obstruction and this rare formation of sigmoido-cecal fistula. It is presented in order to acquaint surgeons with the possibility of an unexpected course of this disease which indeed necessitates an individualized management.