The Mayo Score for Ulcerative Colitis was developed by Schroeder and colleagues in 1987 as the primary clinical endpoint in the first RCT of oral 5-aminosalicylic acid for mild-to-moderate UC. It rapidly became the most widely used activity index in UC clinical trials and clinical practice. The score incorporates four subscores (stool frequency, rectal bleeding, endoscopic findings, physician's global assessment), each scored 0-3, giving a total of 0-12. The endoscopic subscore is the most objective and correlates best with mucosal healing. The partial Mayo score (without endoscopy, 0-9) is used for outpatient monitoring.