Background:Acute cholangitis varies in severity from a mild form to severe cases which require urgent biliary decompression.Aim:This study was undertaken in order to develop a prognostic scoring system that can be used to predict which patients are likely to require emergency endoscopic retrograde cholangiopancreatogram (ERCP) upon admission.Methods:This is a prospective study of 142 consecutive patients with acute cholangitis. Emergency ERCP was performed in patients who did not respond to medical therapy.Results:Thirty‐one patients (21.8%) required emergency ERCP. A maximum heart rate of more than 100/min, albumin of less than 30 g/L, bilirubin of more than 50 μmol/L and prothrombin time of more than 14 s on admission were associated with failure of medical treatment and the need for emergency ERCP (P=0.001, < 0.001, 0.006 and 0.004, respectively). By using these four factors in a scoring system, 50.7% of those with a score of one or more required emergency ERCP compared with 1.5% of those with none of the four risk factors (P < 0.001). This scoring system has a sensitivity of 96.8% and a specificity of 59.6%.Conclusions:As patients with severe acute cholangitis show a higher mortality, we recommend that emergency ERCP be performed in patients with one or more of the four prognostic factors.