Purpose: Several scoring systems and biochemical markers have been proposed for the early prediction of acute pancreatitis. The Harmless Acute Pancreatitis Score (HAPS) is a novel scoring system to recognize acute pancreatitis patients with a non-severe clinical course. This study was conducted to evaluate the usefulness of HAPS to predict good prognosis of acute pancreatitis in the emergency department (ED). Methods: We retrospectively reviewed the electronic medical records of patients who presented to the ED with acute pancreatitis from January 2010 to December 2011. The parameters constituting HAPS, including physical signs of peritonitis (rebound abdominal tenderness), hematocrit and serum creatinine levels were abstracted. Severe clinical course was defined as having one of the following: mortality while in hospital, necrosis as assessed by contrast CT, need for artificial ventilation or dialysis. The diagnostic performance of HAPS for predicting harmless course was evaluated by sensitivity, specificity, and predictive values. Results: During the study period, 144 patients with a final diagnosis of acute pancreatitis were included. Among these 144 patients, 79 were predicted to have a non-severe course by HAPS, of whom 4 patients progressed to severe pancreatitis. The sensitivity, specificity, positive and negative predictive values were 61.5%, 81.8%, 94.9% and 27.7%, respectively. Conclusion: This study suggests that HAPS is simple and can be assessed within a few hours in the ED. HAPS also showed a high positive predictive value that predicts a nonsevere course of acute pancreatitis. Therefore, HAPS may be used as a scoring system to identify non-severe acute pancreatitis in the ED.