Ulcerative colitis (UC) is a chronic inflammatory bowel disease (IBD) characterized by continuous mucosal inflammation of the colon, typically starting from the rectum. Intestinal (bowel) ultrasound (IUS) has emerged as a valuable non-invasive tool for both the initial evaluation and follow-up of UC. IUS enables the assessment of disease extent, activity, and complications by identifying typical ultrasonographic features such as colonic wall thickening, loss of haustration, preserved wall stratification, and mesenteric changes. Transperineal ultrasound (TPUS) further allows evaluation of the rectum, overcoming one of the main limitations of conventional IUS. Wall thickness and Doppler flow are the most reliable indicators of disease activity, with validated scoring systems correlating well with endoscopic findings. In the follow-up of UC patients, IUS proves effective in evaluating response to therapy, with transmural remission defined by a bowel wall thickness ≤3 mm and absence of Doppler signal. Furthermore, IUS can aid in the differential diagnosis of colitis and detect complications such as stenosis, toxic megacolon, or possible neoplastic transformation.