Objective: To examine recent trends in the use of thrombolytic therapy in elderly patients who have had acute myocardial infarction and to determine whether failure to meet time-to-hospital presentation and electrocardiographic criteria might explain age-related differences in the use of thrombolytic therapy. Design: A national registry of patients who have had acute myocardial infarction. Setting: 1249 U.S. hospitals. Patients: 350 755 patients who had an acute myocardial infarction from 1 July 1990 to 30 September 1994. Measurements: Trends in the proportions of patients who received thrombolytic therapy were examined according to age and sex. The association between age and treatment with a thrombolytic agent was determined by crude and multivariable-adjusted analyses. Results: Use of a thrombolytic agent was inversely related to patient age: Almost 51% of patients younger than age 55 years received a thrombolytic agent during hospitalization for acute myocardial infarction; this proportion decreased to 43.6% for patients aged 55 to 64 years, 33.0% for those aged 65 to 74 years, 19.0% for those aged 75 to 84 years, and 7.4% for those aged 85 years or older. However, relative increases in the use of thrombolytic therapy over time were greatest for patients in the oldest age groups. Between 1 July 1990 and 30 June 1991, 16.0% of patients aged 75 to 84 years received a thrombolytic agent compared with 21.4% between 1 June 1993 and 30 September 1994 (a 33.8% relative increase in use). Among persons aged 85 years or older, the proportion of treated patients increased from 5.3% to 9.1% over this same period (a 71.7% relative increase in use). Increases in thrombolytic use were most prominent for older women. After adjustment for sex, diagnosis by initial electrocardiogram, electrocardiogram-based infarction description, time from symptom onset to hospital presentation, and period of the acute myocardial infarction, the odds of receiving a thrombolytic agent were significantly reduced for patients in the older age groups compared with the odds for patients younger than age 55 years (for patients aged 75 to 84 years, the adjusted odds ratio was 0.27 [95% CI, 0.26 to 0.28]; for patients aged 85 years or older, the odds ratio was 0.09 [CI, 0.08 to 0.10]). Conclusions: Although older patients who have had acute myocardial infarction less commonly receive a thrombolytic agent, use of thrombolytic therapy in this population is expanding. However, substantial differences across age groups persist in the likelihood of receiving treatment, even after adjustment for potentially confounding factors. Age- related differences in thrombolytic use may not be completely explained by the degree to which older patients do not meet conventional eligibility criteria for thrombolytic therapy.