Background Many elderly patients with an acute myocardial infarction (AMI) do not receive thrombolysis within 30 minutes of hospital arrival as recommended by the American College of Cardiology/American Heart Association Guidelines. We sought to identify factors associated with delay in administration of thrombolysis after arrival to the hospital in these patients and to determine whether this delay is associated with increased mortality rates. Methods and Results: By using the Cooperative Cardiovascular Project database, we identified patients who received thrombolysis for an AMI. The patients were stratified into groups by time to thrombolysis after hospital arrival. Among a cohort of 17,379 patients, 22.2% received thrombolysis in the first 30 minutes after hospital arrival. Patients treated after the first 30 minutes were more likely to be older, be female, be diabetic, have a history of hypertension or heart failure, and have less marked ST elevation. They were also more likely to be admitted to smaller hospitals with a lower volume of AMIs and to hospitals without a cardiac catheterization laboratory. The 30-day mortality rate was significantly lower for patients treated within the first 30 minutes. After adjustments were made for clinical and hospital characteristics, delays in therapy beyond 30 and 90 minutes were associated with an increase in 1-year mortality rates of 9% and 27%, respectively, compared with delays for patients treated within 30 minutes. Conclusions: After hospital arrival, time to treatment with thrombolytic therapy is longer than recommended in a significant proportion of patients. Clinical characteristics and institutional factors are associated with the delay in treatment. The more rapid treatment of appropriate elderly patients with an AMI probably will reduce mortality rates. (Am Heart J 2000;139:985-92.)