Elective replacement of the aortic root in patients with Marian syndrome is indicated to prevent aortic dissection and prevent left ventricular failure from aortic regurgitation. The two most important factors bearing on the patient's risk for aortic dissection are the maximal aortic root dimension and a family history of aortic dissection. Improvements In surgical technique, favorable long-term postoperative results, and the observation that a substantial proportion of Marian patients die of aortic dissection with an aortic root dimension in the 50-to 60-mm range have led to new recommendations. Asymptomatic Marian patients may be followed annually with echocardiography. When the aortic root dimension reaches 50 mm, the interval between examinations should be shortened to every 3 to 4 months. Asymptomatic individuals with aortic root dimension between 50 and 55 mm should be referred for elective composite graft repair if one or more of the following additional factors are present: moderately severe aortic regurgitation, severe mitral regurgitation, a family history of aortic dissection, and a future need for other major operative procedures such as abdominal aortic aneurysm repair or spinal fusion. In the absence of these factors, asymptomatic individuals may be followed until the aortic root dimension is 55 mm and should then be referred for surgery. Symptomatic individuals with or without aortic root dilatation should be operated upon urgently If evidence of an aortic dissection is present. Postoperatively, all patients should be maintained on beta blockade indefinitely and receive prophylactic parenteral antibiotics before dental, genitourinary, or gastrointestinal procedures. (J Card Surg 1994;9[Suppl]:174–176)