BACKGROUND: Acute myocardial infarction (AMI) with in-hospital onset (AMI-IHO) has poor prognosis but is clinically underap-preciated. Whether its occurrence has changed over time is uncertain. METHODS AND RESULTS: Since 1987, the ARIC (Atherosclerosis Risk in Communities) study has conducted adjudicated surveillance of AMI hospitalizations in 4 US communities. Our analysis was limited to patients aged 35 to 74 years with symptomatic AMI. Patients with symptoms initiating after hospital arrival were considered AMI-IHO. A total of 26 678 weighted hospitalizations (14 276 unweighted hospitalizations) for symptomatic AMI were identified from 1995 to 2014, with 1137 (4%) classified as in-hospital onset. The population incidence rate of AMI-IHO increased in the 4 ARIC communities from 1995 through 2004 to 2005 through 2014 (12.7—16.9 events per 100 000 people; P for 20-year trend 65
