The relation of treatment adherence to mortality after a myocardial infarction was investigated among 2175 participants in the Beta Blocker Heart Attack Trial, which had data for measures of treatment adherence, clinical severity, and the psychological and social features that may influence post-infarction mortality. Overall, patients who did not adhere well to treatment regimen (ie, who took less than or equal to 75% of prescribed medication) were 2.6 times more likely than good adherers to die within a year of follow-up (95% confidence interval, 1.2, 5.6). Poor adherers had an increased risk of death whether they were on propranolol (OR = 3.1) or placebo (OR = 2.5). Furthermore, this increased risk of death for poor adherers was not accounted for by measures of the severity of myocardial infarction, sociodemographic features (eg, race, marital status, education), smoking, or psychological characteristics (high life-stress or social isolation).