This study aims to evaluate the capacity of the clinical and radiological findings and the extrapancreatic necrotic tissue volume in early (2–6 days) computerized tomography (CT) images of patients diagnosed with AP to predict reliably the temporary or permanent organ failure and other local or systemic complications due to pancreatitis. Adult patients who were diagnosed with AP based on Revised Atlanta classification and underwent abdomen CT scans between May 2015 and May 2018 were examined retrospectively. Extrapancreatic necrosis volume was compared to various clinical parameters that indicate the prognosis of AP such as C-reactive protein (CRP) at 48–72th h, organ failure, infection, requirement for percutaneous or surgical intervention, length of hospital stay, and mortality, and to various imaging-based scoring systems such as the computerized tomography severity index (CTSI) and the modified CTSI (mCTSI). The receiver operating characteristic (ROC) curve was used to estimate the optimal threshold for predicting clinical prognosis. Extrapancreatic necrosis volume had moderate positive correlation with length of hospital stay (p = 0.0001) and CRP (at 48–72th h) (p = 0.0001) and strong positive correlation with CTSI (p = 0.0001), mCTSI (p = 0.0001), and white blood cell count (p = 0.0001). Extrapancreatic necrosis volume was found to be particularly better in predicting organ failure and infection compared to the imaging-based scoring systems (Balthazar, CTSI, and mCTSI) and the laboratory-based scoring systems (CRP at 48–72th h).