Adults with bicuspid aortic valves (BAVs) are at risk for progressive aortic dilation independent of valve function. The evolution of aortic dilation in children with functionally normal BAVs has not been studied. In this study, ascending aortic diameters were assessed in a group of children with functionally normal BAVs (peak gradient < or =16 mm Hg) to determine whether progressive dilation occurs during childhood. A cohort of 101 patients and 97 controls were studied with echocardiography. There were no differences in mean age (9.0 +/- 4.8 vs 8.7 +/- 6.1 years, p = 0.7) or body surface area (1.1 +/- 0.4 vs 1.1 +/- 0.5 m2, p = 0.9). Patients had significantly greater aortic dimensions than controls in all measured regions of the aorta, with the most striking discrepancy in the ascending aorta (2.3 +/- 0.6 vs 1.8 +/- 0.5 cm, p <0.0001). The size discrepancy was present from birth and persisted throughout childhood. Repeated measurements were performed in a subgroup of 28 patients and 25 controls. Patients had significantly greater increases in ascending aortic dimension than controls per year of follow-up (1.2 +/- 0.08 vs 0.6 +/- 0.08 mm/year, p <0.0001). In conclusion, BAV is complicated by progressive aortic dilation beginning in childhood.