Serial echocardiographic measurements of the annulus and sinus were obtained in children before the Ross operation, and early and late postoperatively. Values were compared with normal standards for the aorta and pulmonary artery (PA). There was no significant difference between PA annulus measurements before surgery and the corresponding autograft immediately afterward (1.73 ± 0.60 cm preoperatively; 1.63 ± 0.58 cm postoperatively, p = NS). Late after surgery the mean annulus diameter was enlarged compared with the normal aorta (ΔZ 1.9 ± 2.4), but remained relatively unchanged compared with the normal PA (ΔZ 0.7 ± 1.1, p <0.01). In contrast, the autograft sinus was dilated early after surgery (1.83 ± 0.58 cm preoperatively; 2.18 ± 0.73 cm postoperatively, p <0.01). Mean sinus Z score further increased compared with both the aorta (ΔZ 1.3 ± 1.7) and PA (ΔZ 1.3 ± 1.6). Use of standard PA measurements may be important in the assessment of autograft enlargement. Minimal change in autograft Z scores over time suggests that annulus enlargement is mainly due to somatic growth. In contrast, the autograft sinus showed an immediate and continued disproportionate increase in size over time, suggesting that sinus enlargement is largely due to passive dilation.