The objective of this study was to calibrate the national database of short-stay hospitalizations (PMSI MCO) for the surveillance of hospitalized myocardial infarctions. To this end, the PMSI MCO was compared with data collected by the three MONICA registries, for the corresponding age groups and regions. All cases of hospitalized myocardial infarction occurring in 2003 were included, involving individuals aged 35 to 74 years and residing in a region covered by a MONICA registry (the Lille metropolitan area, and the departments of Haute-Garonne and Bas-Rhin). Initially, anonymous discharge summaries (RSA) from the 2003 PMSI MCO database with a primary diagnosis of myocardial infarction and meeting these age and residence criteria, as well as hospital stays from the 2004 database that may have begun in late 2003, were selected. In a second step, these RSAs were sent to the medical information departments of the relevant hospitals or clinics for additional information on the patients’ identities and dates of hospitalization, with the exception of RSAs from facilities that had fewer than 6 hospital stays for myocardial infarction. These completed files were then sent to the registries for comparison with their own records, before being returned to the InVS for verification and analysis. When there were multiple RSA records per event, only a single episode was counted per 28-day period, as is the case for the MONICA registries. The exchange of personal data was encrypted. Among the hospitalized myocardial infarctions assessed by the registries in 2003, 76.2% were identified in the 2003 PMSI: sensitivity was slightly higher among those aged 35 to 64 (80.3%), but decreased among those aged 65 to 74 (69.2%, p<10⁻⁴). Among the myocardial infarctions identified in the PMSI, 78.8% were recorded in the 2003 registry database (positive predictive value) and 21.2% were assessed as false positives. The number of myocardial infarctions estimated by the PMSI based on a single episode per 28-day period was slightly lower than the number of AMIs collected by the MONICA registries (-3.3%). This result varied with age, with the underestimation being greater among those aged 65 to 74 (-8.9%). Conversely, including all emergency department visits with a primary diagnosis of myocardial infarction, including transfers or hospitalizations lasting less than 24 hours, resulted in an overestimation of the number of myocardial infarctions occurring among those aged 35–74 (+12.7%). Comparing the 2003 PMSI MCO data with data from the three MONICA registries allowed us to estimate the PMSI’s sensitivity at 76.2% and its positive predictive value at 78.8% for age groups between 35 and 74 years. In these age groups, the number of myocardial infarctions calculated based on one episode per 28-day period slightly underestimated the total number of myocardial infarctions (-3.3%), whereas including all hospital admissions with a primary diagnosis of myocardial infarction overestimated this number by 12.7%. (R.A.)