Readmission to the hospital within 30 days of discharge (30-day readmission rate) is used as a quality measure.To investigate the incidence and factors that contribute to readmissions in patients with acute cholangitis.Retrospective cohort study.Tertiary-care referral center.Retrospective analysis of consecutive patients admitted to our center for acute cholangitis and ERCP.ERCP.Incidence and variables associated with 30-day readmission and 1-year mortality.ERCP was successful in 98.8% of patients during the index admission. The 30-day readmission rate was 22.0%. Recurrence of cholangitis was the most common etiology for readmissions (37.8%). Readmission within 30 days was independently associated with failed ERCP or ERCP delayed for >48 hours (odds ratio [OR] 2.47; 95% confidence interval [CI], 1.01-6.07), development of any after-ERCP adverse event (OR 11.0; 95% CI, 3.06-39.30), and the etiology of cholangitis (etiologies not related to stones) (OR 3.3; 95% CI, 1.17-9.18). Every 1-point increase in the Charlson Comorbidity Index score (OR, 1.33; 95% CI, 1.05-1.69) was associated significantly with 1-year mortality. In unadjusted analysis, 30-day readmission after ERCP was associated significantly with 1-year mortality (OR, 2.86; 95% CI, 1.16-7.07). This association, however, was not present after adjustment for other covariates.Retrospective study.Delays in performing ERCP during the index admission, development of after-ERCP adverse events, and etiology of cholangitis not related to stones increased the risk of 30-day readmissions.