The clinical, cardiac, and echocardiographic test results of 20 children with marfanoid features are reviewed. Fifteen were diagnosed as having Marfan syndrome, two had "possible" Marfan syndrome, and three had other diagnoses. On first evaluation, eight patients with Marfan syndrome (53%) had mitral regurgitation and none had aortic regurgitation. Echocardiography showed aortic root enlargement in 12 (80%) of 15 patients and mitral valve prolapse in 12 (80%) of 15. None had a normal echocardiogram. At follow-up examination, one patient had developed aortic root enlargement, and one patient, mitral valve prolapse. Thus, although aortic root enlargement is usually present in early childhood in patients with Marfan syndrome, it is not considered specific because in this study it also occurred in one child with Alport's syndrome and in one with marfanoid features. Four patients with aortic root enlargement were treated with propranolol and their echocardiograms showed no further increase in the aortic root diameter for several years. We recommend echocardiography in the diagnosis and routine management of children in whom Marfan syndrome is suspected.