The Japanese severity score (JSS) for acute pancreatitis was revised in 2008. As special therapies for severe acute pancreatitis (SAP), continuous regional arterial infusion of protease inhibitor and antibiotics (CRAI) and enteral nutrition (EN) are now utilized in Japan. We investigated the usefulness of the new JSS and the indications for CRAI and EN based on the new JSS. We assessed the new JSS in 138 patients with SAP according to the previous Japanese criteria. Usefulness of the new JSS for the prediction of mortality rates was compared with conventional scoring systems by receiver-operator characteristic curve analysis. We analyzed the relationship between the new JSS and prognosis in patients with and without CRAI and EN, respectively. Forty-five patients (33%) were assessed as having mild acute pancreatitis, and 93 patients (67%) were assessed as having SAP. Their mortality rates were 7 and 40%, respectively. The area under the curve for the prediction of mortality rates with the new JSS was 0.822 and was the highest among conventional scoring systems. In patients with new JSS >or= 6, the mortality rate was lower in patients with CRAI than in patients without CRAI (P = 0.129). In patients with new JSS >or= 4, the mortality rate was lower in patients with EN than in patients without EN (P = 0.016). The new JSS is useful and easier to use for the prediction of prognosis compared to the conventional scoring systems. EN was effective in reducing the mortality rate in patients with a new JSS >or= 4.