The Worcester Heart Attack Study is an ongoing population-based investigation examining changes over time in the incidence and case-fatality rates of acute myocardial infarction (AMI) in residents of metropolitan Worcester, Massachusetts. Using this large population-based database of patients with independently validated AMI, we examined the impact of the September 11th tragedy on the occurrence rates of AMI in residents of greater Worcester presenting to all area hospitals during 2001 compared with rates in the previous 10 years.