The severity of acute pancreatitis (AP) is classified into mild, moderately severe, and severe, considering the presence and duration of organ failure and local complications. Since patients with AP show a large difference in mortality and morbidity according to AP severity, evaluation of the severity of patients with AP in the early stage is important for predicting the prognosis and determining treatment plans including transfer to the intensive care unit or advanced facilities. In order to evaluate the initial severity of AP, it is necessary to confirm the presence of organ failure and objective evaluation using imaging or clinical examinations. In this guideline, it is recommended that evaluation using various severity indices such as bedside index for severity in acute pancreatitis (BISAP), systemic inflammatory response syndrome (SIRS), and acute physiology and chronic health evaluation (APACHE)-II scores be considered.