Background: This prospective study was conducted between January 2015 and June 2018 and included 50 patients (mean age of 52.12 ± 2.0 years), all presented with acute pancreatitis and admitted to the ICU 1–3 days after the onset. All patients underwent contrast-enhanced CT, and images are evaluated by 2 independent radiologists for the modified CTSI parameters and retroperitoneal extension parameters to detect the severity of pancreatitis. The aim of this study is to compare the results of the modified CT severity index and retroperitoneal interfascial extension CT grading system in the grading of the severity of acute pancreatitis and compare both grading systems to the clinical course of the disease and its complications. Results: Both grading systems show a statistical significant correlation in terms of the length of hospital stay, the need for interventions, and the development of organ failure. Conclusion: In conclusion, a good correlation was observed between the modified CTSI and retroperitoneal extension grading systems in grading the severity of acute pancreatitis. We think that we can apply Ishikawa et al. grading system as a prognostic indicator if there is a contraindication to contrast administration. Keywords: Modified CT severity index, Acute pancreatitis, Retroperitoneal interfascial planes, Severity of acute pancreatitis, Grading of acute pancreatitis