To determine the association of Type A behavior and coronary heart disease risk factors in children with a familial predisposition for premature atherosclerosis, subjects 6 to 16 years of age were evaluated on psychological and coronary risk measures. Subjects were classified as being Type A or Type B using the Student Structured Interview. Type A subjects had lower total serum and LDL cholesterol levels and lower systolic and diastolic blood pressure than Type B subjects. In addition, Type A subjects had more social competence skills and less behavioral disturbance relative to Type B subjects. Type A subjects tended to have better endurance on treadmill stress testing. These results suggest that in children with increased risk for coronary artery disease, the Type A behavior pattern may be associated with better fitness, better psychological health, and lower serum cholesterol levels. We hypothesized that the psychological and physiological characteristics of children with Type A behavior may enable them to adopt hygienic lifestyles more readily than children with Type B behavior.