Until recently, surgical correction of Marfan defects of the aortic root has been undertaken with some hesitancy because of the high perioperative risk. The Division of Medical Genetics at Johns Hopkins follows about 300 patients with the Marfan syndrome, and during the past 8 years 13 of these were referred to the senior author (V.L.G.) for aortic valve replacement and repair of the ascending aorta. Preoperatively, four of the 13 patients were in New York Heart Association (NYHA) Class IV (3/4 required emergency operation), three patients were in Class III, and six were in Class II. The aortic diameter at the mid-valve level ranged from 5.3 cm to 8.2 cm on M-mode echocardiography. The first two patients received a separate Björk-Shiley prosthesis and a woven Teflon graft and the last 11 patients had a composite valve-graft with direct coronary implantation. There were no hospital deaths. Follow-up ranges from 6 months to 8.1 years and is complete for all 13 patients (mean of 23 months). Two late deaths occurred 2 and 20 months postoperatively from presumed arrhythmia and two late deaths occurred at 4 and 6 months from endocarditis. The actuarial survival rate at 3 years is 61%. Some pathologists claim that the incidence of dissection of the aorta does not increase with increasing aortic dilatation in the Marfan patient. Six of our 13 patients, however, had aortic dissection at the time of surgery (two DeBakey Type I, three Type II, and one Type III). With the low hospital mortality that can now be achieved in the Marfan patient, and with the relatively high incidence of clinically unrecognized dissection, we fell that strong consideration should be given to earlier prophylactic repair in these patients. Operation may be indicated even in the asymptomatic Marfan patient with an aortic root diameter greater than 5.5 cm.