Very early administration of thrombolytic therapy for acute myocardial infarction (AMI) has significantly reduced mortality in eligible patients. The purpose or this study was to evaluate factors which influenced the time from symptom onset to hospital presentation and the time from hospital presentation to the onset of thrombolytic treatment in a large population of patients with AMI. This study included 212,990 patients from 904 hospitals that participated in the National Registry of Myocardial Infarction. The median time from symptom onset to hospital presentation for those treated was 1.5 hours versus 2.7 hours for those not receiving thrombolytic treatment. Older patients and women had increased delay rimes, as did those who arrived at the hospital during daytime hours. Of the 59,802 (28%) patients who received thrombolytic treatment, 23% were treated <30 minutes from admission; 63%, <60 minutes; and 83%, < 90 minutes. Time to treatment increased with age and was longer for women and for patients arriving between midnight and early morning. The most important factor associated with shorter time to treatment was the initiation of thrombolytic treatment in the emergency department rather than in the coronary care unit (47 vs 73 minutes, p < 0.0001). Hospital treatment times are much too long, given that quick identification and treatment of eligible patients are of primary importance in reducing mortality from AMI. To shorten these times, thrombolytic treatment should be initiated in the emergency department, and the effectiveness of hospital programs aimed at reducing time to treatment should be subject to continuing quality improvement surveillance. © 1995.