Marfan syndrome (MS) is a connective tissue disease involving the cardiovascular, ocular, and the musculoskeletal systems. MS has variable phenotypic expression and is most often diagnosed in adult life. Infantile-onset MS is rare and is associated with severe cardiovascular manifestations; there is an extremely high mortality during the first 2 years of life. We present a case of a child with severe infantile MS who, during the course of infancy and early childhood, developed aortic root dilatation and polyvalvar insufficiency requiring subsequent successful replacement of the aortic root and of all cardiac valves. To our knowledge, this is the first reported case of quadrivalvar replacement in the pediatric age group.