Ulcerative colitis is a chronic inflammatory bowel disease that affects the colon. It is characterized by inflammation and ulcers in the lining of the rectum and colon. The causes are unknown but likely involve genetic and immune factors. Symptoms include abdominal pain, bloody diarrhea, and weight loss. Diagnosis involves blood tests, colonoscopy, and biopsy. Treatment focuses on reducing inflammation through medications like mesalamine, corticosteroids, immunosuppressants, or biologics. Surgery to remove the colon may be needed for severe cases or cancer prevention. Complications can include toxic megacolon, colon cancer, and extraintestinal manifestations.