BACKGROUND: The utility of intestinal ultrasound (IUS) for ASUC is understudied. We correlated IUS to clinical, biochemical, and endoscopic disease severity in ASUC. METHOD: In a blinded, prospective study of 20 ASUC subjects, we analyzed standard IUS parameters (bowel wall thickening, vascular flow, wall stratification) and UC IUS indices (IBUS-SAS, Milan-UC, UC-IUS) alongside modified Mayo symptoms scores, C-reactive protein (CRP), albumin, and UC endoscopic index of severity (UCEIS). Spearman correlations were performed (rs). Areas under the curve (AUC) determined utility of IUS for detecting severe endoscopic disease. RESULTS: All IUS indices correlated with stool frequency (rs:0.45-0.58, p<0.001), CRP (rs:0.56-0.59, p<0.02), and UCEIS (rs:0.54-0.69, p<0.03). IBUS-SAS (AUC 0.91) and Milan-UC (AUC 0.93) outperformed IUS-UC (AUC 0.82) for detecting UCEIS>5. Loss of bowel wall stratification correlated strongest with CRP (rs: 0.8, p=3.61e-8) and UCEIS (rs: 0.50, p=0.047). CONCLUSION: IUS offers an accurate and non-invasive method to evaluate ASUC severity and treatment response.