OBJECTIVES:Acute severe ulcerative colitis (ASC) is a potentially life-threatening disease. We aimed to formulate guidelines for managing ASC in children based on systematic review of the literature and robust consensus process. This manuscript is a product of a joint effort of the ECCO (European Crohn's and Colitis Organization), the Pediatric Porto Inflammatory Bowel Disease (IBD) Working group of ESPGHAN (European Society of Pediatric Gastroenterology, Hepatology, and Nutrition) and ESPGHAN.METHODS:A group of 19 experts in pediatric IBD participated in an iterative consensus process including two face-to-face meetings. A total of 17 predefined questions were addressed by working subgroups based on a systematic review of the literature.RESULTS:The recommendations and practice points were eventually endorsed with a consensus rate of at least 95% regarding: definitions, initial evaluation, standard therapy, timing of second-line therapy, the role of endoscopic evaluation and heparin prophylaxis, how to administer second-line medical therapy, how to assess response, surgical considerations, and discharge recommendations. A management flowchart is presented based on daily scoring of the Pediatric Ulcerative Colitis Activity Index (PUCAI), along with 28 formal recommendations and 34 practice points.CONCLUSIONS:These guidelines provide clinically useful points to guide the management of ASC in children. Taken together, the recommendations offer a standardized protocol that allows effective monitoring of disease progress and timely treatment escalation when needed.