One of the main advantages of an aortic valve homograft in comparison with a mechanical prosthesis is the low incidence of thromboembolism without anticoagulation. Development of an obstructive thrombosis is virtually unknown. We report the case of a patient who twice was seen with hemodynamically significant thrombosis of an aortic valve homograft. The diagnosis was suspected on the basis of a subacute increase in the transvalvular gradient and was confirmed by transesophageal echocardiography. Lupus anticoagulant antibodies were detected. Oral anticoagulation proved to be effective in relieving the obstruction, but recurrence after discontinuation of acenocoumeral suggests that treatment should be long term, if not lifelong. To our knowledge, this complication of primary antiphospholipid syndrome is the first reported case of thrombotic obstruction of an aortic valve homograft.