Functional tricuspid regurgitation (TR) is usually due to pulmonary hypertension with subsequent right ventricular and tricuspid valve anular dilatation. The correlation between anular dilatation and TR severity is unclear. Unfortunately, there is no simple, accurate method of assessing the presence and severity of TR. Real-time (color flow) Doppler echocardiography, a sophisticated but expensive technique, facilitates noninvasive determination of the presence and severity of TR by the area and depth of color-encoded, systolic turbulent reflux into the right atrium. In this study, TR severity (0 to 4+), assessed by color flow Doppler, was correlated with diastolic and systolic tricuspid valve anulus dimension, measured by computerized calipers, from the apical 4-chamber and right ventricular inflow 2-dimensional views. Forty-six patients were studied: 32 with 0 to 2+ TR and 14 with functional 3 to 4+ TR. TR severity correlated significantly with the tricuspid valve anulus in both diastole and systole. The correlation was best in the apical 4-chamber view during systole (r = 0.88, p less than 0.0001). No patient with tricuspid valve anulus in systole less than 3.2 cm or in diastole less than 3.4 cm had severe (3 to 4+) TR. Thus, measurement of the tricuspid valve anulus by 2-dimensional echocardiography is a simple, noninvasive method to identify patients with moderate to severe TR.