Pancreatic pseudocyst due to blunt abdominal trauma is a rare case. When enlarging, it obstructs the gastric outlet resulting in malnutrition. If leaking into the abdomen, it causes peritonitis(1). This study is intended to present the case of SIRS caused by a leakage pancreatic pseudocyst with malnutrition successfully treated based on the principles of Acute Care Surgery and ESPEN Nutritional Therapy(2). An 18-year-old male was admitted to the emergency department with abdominal pain, vomiting, and fever. In the specific examination, tachycardia, underweight, and a “Cullen Sign” on the anterior abdominal wall were found. After initial management, definitive surgery was performed immediately including a gastrocystostomy as decompressive management with damage control surgery including abdominal lavage and antibiotic escalation. Postoperatively, nutritional management was undergone using a step-up calorie approach based on the patient’s condition(2). Octreotide had been established for four days as a management for pancreatitis. Nutritional management proceeded until the fourth regular control after the patient showed an increase in BMI. Acute care surgical principles suggest a survival benefit in this case. The success of treatment in this patient was an improvement in clinical and nutritional status. References: 1. Son TQ, Hoc TH, Huong TT, Dinh NQ, Van Tuyen P. A ruptured pancreatic pseudocyst causes acute peritonitis with clinical characteristics of a gastrointestinal tract perforation. J Surg Case Rep. 2022 May 1;2022(5). 2. Arvanitakis M, Ockenga J, Bezmarevic M, Gianotti L, Krznarić Ž, Lobo DN, et al. ESPEN guideline on clinical nutrition in acute and chronic pancreatitis. Clinical Nutrition. 2020 Mar 1;39(3):612–31.