To determine the relationship between Type A behavior pattern and angiographically documented coronary atherosclerosis (CAD), we analyzed risk factor, behavioral, and angiographic data collected on 2,289 patients undergoing diagnostic coronary angiography at Duke University Medical Center between 1974 and 1980. Multivariable analyses using ordinal logistic regression techniques showed that Type A behavior as assessed by the structured interview (SI) is significantly associated with CAD severity after age, sex, hyperlipidemia, smoking, hypertension, and their various significant interactions were controlled for. This relationship, however, is dependent upon age. Among patients aged 45 or younger, Type A's had more severe CAD than did Type B's; among patients aged 46-54, CAD severity was similar between Type A's and B's; and among patients 55 and older, there was a trend toward more severe CAD among Type B's than among Type A's. These Type A-CAD relationships did not appear to be the result of various factors relating to the selection of patients for angiography. Type A behavior as assessed by the Jenkins Activity Survey was unrelated to CAD severity. These findings suggest that SI-determined Type A behavior is associated with more severe CAD among younger patients referred for diagnostic coronary angiography. The reversal of the Type A-CAD relationship among older patients may be due to survival effects. Inadequate sample sizes, use of assessment tools other than the SI, and failure to consider the Type A by age interaction could account for failures to find a Type A-CAD relationship in other studies. We conclude that the present findings are consistent with the hypothesis that Type A behavior is involved in the pathogenesis of CAD, but only in younger age groups. The Type A effect in the present data is small relative to that of both smoking and hyperlipidemia, however, and future research should focus more specifically on the hostility and anger components of Type A behavior, particularly in younger samples.