Sigmoidoscopy (or sigmoidoscope) is an examination of the inside of the rectum (back passage) and colon (large bowel) as far as the sigmoid colon. The sigmoid colon is the S shaped part of the large bowel on the lower left of the abdomen. The doctor puts a sigmoidoscope (a thin bendy tube) into the bowel through the anus. It can take biopsies (samples of tissue) for examination under the microscope.