Although appendiceal tumours are rare, they may be encountered unexpectedly in any emergency abdominal operation. Many of these tumours are not recognized intraoperatively and are diagnosed only during formal histopathological analysis of an appendectomy specimen. We present a rare case of appendiceal adenocarcinoma which caused acute bowel ob struction. The patient presented with abdominal pain, distension and constipation. Abdominal radiography showed large bowel obstruction. On laparotomy the appendix was abnormal, with a tumor growing in to the ileal loop and creating a bowel obstruction. An appendectomy was performed with enbloc bowel segment resection and end ileostomy. Pathology specimens showed that the primary neoplasm was the appendiceal mucinous adenocarcinoma infiltrating the ileal loop. Patient underwent a right hemicolectomy, and recovered afterwards with no evidence of local recurrence or metastatic disease as confirmed by the standard follow-up. Physicians should keep in their minds that appendiceal neoplasm may have various and nonspecific presentations, but only an accurate diagnosis will lead to correct patients treatment, healing and long-term survival