ABSTRACT Objectives: Acute diverticulitis is increasingly common in emergency departments. While CT is frequently used, the 2021 German guidelines do not specify whether ultrasound (US) or CT is superior for diagnosis. We evaluated the diagnostic accuracy of US performed by attending surgeons compared to CT for classification and therapeutic decision-making. Methods: This prospective study included 62 patients with suspected acute diverticulitis presenting to the emergency department of German Armed Forces Hospital Ulm, Germany (April 2021–March 2024). All patients underwent US followed by CT (reference standard). US was performed by general surgeons and CT analyzed by radiologists, both blinded to each other's findings. Disease was staged using the 2021 German Classification of Diverticular Disease (CDD). Results: Median age was 55 years (range 27–85), mean BMI 28 kg/m2, 32% female. US diagnosed uncomplicated diverticulitis (CDD Ia/b) in 44 patients (71%), complicated diverticulitis (CDD IIa/b) in 7 (11.3%), and no pathology in 11 (17.7%). CT findings: no diverticulitis in 12 (19.4%), uncomplicated in 38 (61%), and complicated in 12 patients (19.3%). US demonstrated 88% sensitivity and 41% specificity for detecting acute diverticulitis (sensitivity and specificity uncomplicated stages: 76% and 38%; complicated 33% and 94%). Positive predictive value was 86%, negative predictive value 46%. Therapeutic decisions based on US versus CT differed by 4% for both conservative and surgical management (75% vs 79% conservative treatment). Conclusion: US reliably diagnoses uncomplicated diverticulitis and excludes complicated stages with high specificity. US is valid for initial screening to identify patients requiring additional CT imaging. Therapeutic outcomes were nearly identical despite classification differences, suggesting US as first-line imaging can reduce costs, radiation exposure, and resource utilization.