Background: Non-traumatic acute abdomen is a common emergency presentation requiring timely diagnosis to guide appropriate treatment. Clinical assessment alone may not reliably identify the underlying pathology, making imaging essential. Aim: To evaluate the utilisation of ultrasonography (USG) and computed tomography (CT) in the assessment of non-traumatic acute abdomen among adults and compare their diagnostic accuracy and contribution to management. Methods: This prospective observational study included 90 adult patients presenting with non-traumatic acute abdomen. Clinical findings and admission diagnoses were recorded. All patients underwent USG and CT evaluation, and imaging findings were compared with the final diagnosis and, where available, operative findings. Diagnostic accuracy and changes in management following imaging were assessed. Results: The mean age of participants was 42.1 ± 14.2 years, and 62.2% were male. Acute appendicitis was the most common final diagnosis (25.6%), followed by intestinal obstruction and ureteric colic/urolithiasis (13.3% each). The admission clinical diagnosis was correct in 54.4% of cases. Overall diagnostic accuracy was 85.6% for USG and 95.6% for CT; the difference was not statistically significant (p=0.052). Among patients with operative findings, diagnostic concordance was 87.0% for USG and 96.3% for CT. USG was sufficient to guide management in 62.2% of patients, whereas CT altered the management plan in 37.8% and helped avert potentially unnecessary surgery in 11.1%. USG findings were equivocal in 10.0% of cases, while CT findings were indeterminate in 4.4% in the present study. Conclusion: USG is a useful initial investigation for adult patients with non-traumatic acute abdomen, while CT provides additional diagnostic clarity and influences management when further evaluation is required. A selective, sequential imaging approach may support appropriate clinical decision-making.