ASC is a life-threatening medical emergency. The lack of a timely intervention has shown to be associated with a mortality rate higher than 20% in adults, whereas a prompt targeted therapy has displayed a decrease of the aforementioned rate to 1%. Therefore, the identification of predictors of poor outcome trough an objective tool may provide crucial help to individualize the timing of second line treatment initiation. At the state of the art, PUCAI represents the only validated tool to appraise the risk of first-line treatment failure and there is a lack of objective methods with a prognostic value in ASC. BUS has proven to be a reliable tool in assessing disease activity in children with UC and it has also shown statistically significant correlation with endoscopic features of disease activity. Given the literature suggesting a role for BUS in severe UC and the results from our retrospective study we aim to validate our findings trough a prospective assessment of the potential prognostic role of BUS in ASC.