Sigmoidoscopy is a diagnostic procedure used to examine the lower part of the large intestine, specifically the rectum and sigmoid colon. Using a flexible, lighted tube called a sigmoidoscope, doctors can detect issues such as polyps, inflammation, ulcers, and signs of colorectal cancer. It is a quick, minimally invasive procedure often used for screening and diagnosing digestive symptoms like rectal bleeding or chronic diarrhea.