Acute cholangitis complicating diagnostic endoscopic retrograde cholangiopancreatography (ERCP) is potentially fatal. Among 323 consecutive patients with proved biliary obstruction, 21 (7 percent) developed acute cholangitis after examination. Four patients underwent emergency surgery for the control of sepsis with two deaths. Of the 21 parameters chosen for evaluation, malignant obstruction, fever (higher than 37.5 degrees C) within 72 hours before the procedure or when afebrile, and an increased aspartate transaminase level of 70 IU or more were the independent predictive factors identified by multivariate analysis. An increased temperature should be regarded as an absolute contraindication to examination unless followed by immediate ductal drainage. Since the risk of septic complications is minimal when none of the risk factors are present, routine urgent biliary decompression after ERCP is probably unnecessary for these selected patients. For patients with malignant obstruction or other risk factors, early elective surgical drainage is advisable. When surgery is not feasible, nonoperative drainage of the obstructed biliary system as a preventive measure might be considered.