Two-dimensional echocardiographic examinations of the proximal left and right coronary artery were performed in 100 children without heart disease. Fifty-nine boys and 41 girls were studied whose ages ranged from 1 day to 17 years old. The diameter of the proximal right and left coronary artery was 1 mm in newborns and 4.5 mm in teenagers. No significant difference was observed between male and female subjects. A linear correlation between the coronary artery dimensions and the patient's age, weight, length, and body surface area could be demonstrated. The closest linear correlation corresponded to the patient's length with a correlation coefficient of r = 0.91 and r = 0.89 for the right and the left proximal coronary artery respectively. A quick orientation concerning normality of coronary artery diameters is possible with our graph of body length and corresponding coronary artery size. Knowing normal echocardiographic values for proximal coronary artery diameters, even subtle changes of these vessels can be diagnosed and the number of invasive diagnostic procedures, e.g. in Kawasaki disease, can be reduced.