For a long time, the small intestine could not be approached using endoscopic examinations. The development of capsule endoscopy, double balloon enteroscopy and single balloon enteroscopy have made endoscopic examination of the entire small bowel practical. A 68-year-old male patient presented with tarry stool and weakness for one week. Abdominal CT revealed multiple intra-abdominal metastatic tumors. Upper gastrointestinal endoscopy and colonoscopy did not disclose any lesions. We used the recently developed single balloon enteroscope for examination of the small intestine and a jejunal tumor was found that situated 110cm beyond the ligament of Treitz. The pathological diagnosis was a rare undifferentiated carcinoma.