Background: The revised Atlanta classification of 2012 categorizes acute pancreatitis (AP) into mild (MAP), moderately severe (MSAP) and severe (SAP). MSAP is often self-limited and with early treatment it has less complications than SAP. Several severity scoring systems have been developed, however they are cumbersome and complex. An easily applicable scoring system is needed to identify patients that will develop a more severe course, in order to initiate early adequate treatment. The Modified Early Warning Score (MEWS) is a simple, physiological score that is easily used in the regular hospital routine. Our hypothesis was that patients with MSAP have a higher MEWS within the first 48 hours after admission than patients with MAP. Material and Methods: Adult patients with AP admitted to the Department of Surgery, University Hospital of Linköping, Sweden, between 2011 and 2016 were included. Data was prospectively collected into a database and all patients with MAP and MSAP were included in the analysis. Clinical data and laboratory parameters were collected on the day of arrival to the hospital and on the three following days. The study protocol was approved by the local ethical board (dnr 2010/336-31). Results: Eighty-eight patients were included, 68 with MAP and 20 MSAP. There was no significant difference between the groups in age, gender, aetiology and previous AP. The length of hospital stay was longer for MSAP with a median of 9 (range 4-36) compared to MAP 4 (2-9) (p<0,00001). No patients with MAP had MEWS more than 3 on any day of the study. The sensitivity of MEWS < 3 in predicting MAP was 0,96 with a positive predictive value of 0,84. Conclusions: MEWS could be an easily applicable prognostic tool to early differentiate between MAP and MSAP, thereby facilitating early resuscitation and thus preventing more severe outcome of AP.