Summary We compared measures of hospital performance by using both administrative and clinical data sources. Hospital-specific mortality outcomes on 10086 patients who had been admitted to 102 hospitals with a diagnosis of acute myocardial infarction in Ontario, Canada, were used as a test-case. Four and six hospitals were identified as having mortality that was statistically significantly higher than expected by using administrative and clinical data respectively, when model-based indirect standardization was used. When using random-effects models, zero and two hospitals were identified as having significantly higher mortality by using administrative and clinical data respectively. Approximately one in four hospitals changed at least two decile rankings when clinical data were used compared with when administrative data were used.