Introduction: Although endometriosis with sigmoid serosal involvement is not uncommon in women of childbearing age, the mucosal and lymph node involvement is rare and differential diagnosis from colon cancer and diverticulitis may be difficult due to poor diagnostic accuracy of colonoscopy and colonic biopsies.
Case presentation: We present a case of a nulliparous woman presenting with large bowel obstruction. She underwent emergency sigmoid colectomy based on clinical and radiological findings. At operation, the pathology was thought to be primary sigmoid tumour. However, histopathological examination of the sigmoid colon led to the final diagnosis of large intestinal endometriosis.
Conclusion: Rectosigmoid endometriosis is often difficult to diagnose but should be considered in differential diagnosis of child bearing aged women with lower gastrointestinal tract obstruction.