Background: In developing countries with limited healthcare resources, excessive ancillary investigations can waste resources and delay patient care. Deciding which patients need these tests after blunt trauma is critical. The Clinical Abdominal Scoring System (CASS) is reported to predict intra-abdominal injuries from blunt abdominal trauma effectively. Objective: Evaluate the diagnostic accuracy of the clinical abdominal scoring system (CASS) against CT results to predict IAI in blunt abdominal injury victims trauma Design/Setting: A prospective observational study over 11 months was conducted in the General Surgery Department at Agha Khan University Hospital, a level 1 trauma centre in Karachi, Pakistan Participants: All hemodynamically stable adult patients, 18 to 80 years of age with blunt abdominal trauma who presented to the Emergency Department from 1st November 2020 to 2nd October 2021 and underwent complete history and examination by the trauma team members and computed tomography of the abdomen with intravenous contrast were consecutively enrolled. CASS scores were calculated. Results: Of 110 patients, the CT scan of the abdomen showed positive findings in 33 (30%) patients. The CASS scores ranged from 4 to 14 with the maximum number of patients (40) scoring 8 – 9. There were 60 (54.5%) patients with low risk and 50 (45.4%) with high-risk CASS scores. The CASS sensitivity was 84.8%, specificity 71.42%, positive predicted value 56%, negative predicted value 91.67%, and overall diagnostic accuracy was 75.4%. The ROC curve showed AUC as 0.865 (95% 0.78-0.94). Conclusion: High diagnostic accuracy and reliability were observed for CASS to predict intra-abdominal injuries in blunt abdominal trauma patients taking CT results as a gold standard.