Aortic root dilatation is the principal life-threatening complication in Marfan syndrome, leading to aortic regurgitation, dissection, and rupture. Beta blockade slows aortic dilatation in adults, but there has been no definitive evidence in children. Therefore, the evolution of aortic diameter at the level of the sinuses of Valsalva in 155 children (82 males, 73 females) aged <12 years who had been diagnosed with Marfan syndrome according to international criteria was retrospectively studied. Affected children treated by beta blockade >or=1 time during their lives (n = 77, mean age at diagnosis 6.1 +/- 3.2 years) were compared with affected children who had never received beta blockers (n = 78; 42 males, mean age 7.4 +/- 5.2 years). A mean delay of 1.3 years was observed between diagnosis and the initiation of beta blockade in the treated group (mean age at initiation 7.5 years). At the time of diagnosis, aortic diameters were similar in the 2 groups, but after 1.3 years, aortic diameters were greater in the group of children in whom beta blockers had been initiated. On univariate analysis, aortic diameter was related to age and height, but not gender or familial history of aortic dissection. On multivariate analysis, treatment and age remained significant determinants of aortic diameter. Beta blockade significantly decreased the rate of aortic dilatation at the level of the sinuses of Valsalva by a mean of 0.16 mm/year (p <0.05), an effect that increased with treatment duration. A trend toward lower cardiac mortality, decreased need for preventive aortic surgery, and less dissection was observed. In conclusion, beta blockade appears to limit aortic dilatation during childhood in patients affected by Marfan syndrome. Therefore, this treatment should be recommended as soon as the diagnosis is made.