To determine the extent to which the elderly have been excluded from trials of drug therapies used in the treatment of acute myocardial infarction, to identify factors associated with such exclusions, and to explore the relationship between the exclusion of elderly and the representation of women. We conducted a systematic search of the English-language literature from January 1960 through September 1991 to identify all relevant studies of specific pharmacotherapies employed in the treatment of acute myocardial infarction. To accomplish this, we searched MEDLINE, major cardiology textbooks, meta-analyses, reviews, editorials, and the bibliographies of all identified articles. Only trials in which patients were randomly allocated to receive a specific therapeutic regimen or a placebo or nonplacebo control regimen were included for review. Studies were abstracted for year of publication, source of support, performance location, drug therapies to which patients were randomized, use of invasive diagnostic tests or therapeutic procedures, exclusion criteria, size and demographic characteristics of the randomized study population, and principal outcome measures. A total of 214 trials met inclusion criteria, involving 150,920 study subjects. Over 60% of trials excluded persons over the age of 75 years. Studies published after 1980 were more likely to have age-based exclusions compared with studies published before 1980 (adjusted odds ratio, 4.92; 95% confidence interval, 2.33 to 10.54). Trials of thrombolytic therapy involving an invasive procedure were more likely to exclude elderly patients compared with other studies (adjusted odds ratio, 2.45; 95% confidence interval, 1.10 to 5.47). Studies with age-based exclusions had a smaller percentage of women compared with those without such exclusions (18% vs 23%; P = .0002), with the mean age of the study population significantly associated with the proportion of women participants (P = .0001, R2 = .29). Age-based exclusions are frequently used in clinical trials of medications used in the treatment of acute myocardial infarction. Such exclusions limit the ability to generalize study findings to the patient population that experiences the most morbidity and mortality from acute myocardial infarction.