Abstract
A 30-year-old woman with Down's syndrome visited a physician because of bloody stool, diarrhea and abdominal pain. She was diagnosed as enteritis and medicated. However, she had a checkup at another hospital because her symptoms did not improve. Barium enema examination demonstrated a sigmoid colon cancer. So she was admitted to our hospital and underwent sigmoidectomy with lymphnode dissection (D3). She has survived without recurrence as of thirty months after the operation. Patients with Down's syndrome have greater risk of leukemia than the general population, but lower risk of other malignancy, so we report this rare case.