In the differential diagnosis of abdominal pain, acute pancreatitis may be diagnosed by its clinical features together with blood determinations and ultrasonographic findings. The primary diagnostic steps include the differentiation between biliary or non-biliary etiology of the disease. In biliary acute pancreatitis, ERCP with endoscopic sphincterotomy is recommended, although the benefit of this procedure has only been shown in patients with severe clinical courses. An early discrimination between edematous-interstitial pancreatitis [mild clinical course] and necrotizing pancreatitis [severe clinical course associated with local and systemic complications] is possible by daily CRP-monitoring. In necrotizing pancreatitis, contrast-enhanced computed tomography is the next diagnostic step, and the patient should be transferred to an intensive care unit. To differentiate between severe sterile pancreatitis and infected pancreatic necrosis, ultrasonographic or CT-guided fine needle aspiration of the pancreatic inflammatory mass is suggested. Infected pancreatic necroses are associated with systemic septic complications, which are the main mortality factor and the major reason for operative treatment of necrotizing pancreatitis.