Background: The relationship between hospital procedure volume and outcome has been recognized for various specialties and procedures. Although increasingly used and in existence for 40 years, to date, data on the relationship between hospital volume and outcome of ERCP are scant. Objective: We sought to examine health-related outcomes after ERCP in relation to hospital procedure volume. Design: Secondary analysis of a national administrative database. We used the National Inpatient Sample (NIS) database to evaluate health-related outcomes among patients who underwent ERCP from 1998 to 2001. Main Outcome Measurements: Logistic and multiple regression models were used to estimate the association of hospital ERCP volume with length of stay (LOS), rates of procedural failure, and mortality. Fixed effect models were used to adjust for all time invariant hospital characteristics for each hospital within the dataset. Results: Data from 2629 hospitals that performed 199,625 ERCPs were evaluated. The median number of ERCPs performed in participating hospitals was 49 per year (range, 1-1004), with 25% of hospitals performing ≥100 ERCPs per year and 5% performing ≥200 per year. Significant trends in the relationship between volume and outcome were observed with respect to LOS and procedural failure: the median LOS was lower in high-volume (≥200 ERCP/y) than low-volume (≤100 ERCP/y) hospitals (6.9 vs 7.8 days, p < 0.0001) and the mean difference in expected LOS was 1.08 days (p < 0.0001). Multivariate regressions with hospital level fixed effects found significant negative relationships between procedure volume and procedure failure rates, but no significant effect on inpatient mortality rates was detected. Limitations: NIS database permits analyses of only inpatient ERCPs. It precludes analysis of procedural complications, reinterventions, and influence of individual provider volume on outcomes. Conclusions: Inpatients who undergo ERCP at high-volume hospitals have shorter LOS and lower procedural failure rates than those undergoing ERCP at low-volume hospitals. These findings have important implications for health care policy decision making and resource utilization. © 2006 American Society for Gastrointestinal Endoscopy.