Prevalence of aortic regurgitation by color flow Doppler in relation to aortic root size. To determine whether there is a correlation between aortic root size and the prevalence of aortic regurgitation, we performed color flow Doppler echocardiographic studies on 1015 consecutive patients during a 3-month period. Patients were grouped according to their M-mode aortic root diameter as measured in the left parasternal position. The measured groups ranged from 2.0 to 4.5 cm, grouped at 0.1 cm intervals. As the aortic root size enlarged, the prevalence of aortic regurgitation increased linearly (p less than 0.001; correlation coefficient, r = 0.75). At an aortic root size in the "small normal" range of 2.0 to 2.4 cm, the prevalence of aortic regurgitation was 0% to 15%. In the "intermediate" and "top normal" ranges of 2.9 to 3.7 cm, the prevalence of aortic regurgitation increased linearly from 15% to 47%. With aortic root dilation, the prevalence of aortic root regurgitation was generally more than 50%. The severity of aortic regurgitation was semiquantified. Aortic root size was not a good indicator for the severity of aortic regurgitation. Patients with moderate and severe aortic regurgitation had variable aortic root sizes. Throughout the range of aortic root sizes, mild aortic regurgitation predominated. We conclude that aortic regurgitation is a common finding in patients with aortic roots that are dilated or are in the "top normal" size range, that the prevalence of aortic regurgitation increases linearly with aortic root size, and that aortic root size does not correlate with the severity of aortic regurgitation. 