SummaryIntroduction:This prospective study was planned to investigate the frequency and relationship of acquired von Willebrand syndrome (AVWS) with aortic and pulmonary stenosis in patients.Methods:A total of 84 children, ranging from two to 18 years of age, were enrolled in this study. Of these, 28 had isolated aortic stenosis, 32 had isolated pulmonary stenosis and 24 were healthy. Children with aortic and pulmonary stenosis associated with other congenital heart diseases were excluded. Children with hypothyroidism, renal or liver disease, malignancy or autoimmune disease were also excluded. Wholeblood count, blood group, factor VIII level, prothrombin time (PT), activated partial thromboplastin time (aPTT), von Willebrand factor antigen (VWF:Ag), ristocetin co-factor (VWF:RCo), and bleeding time using a platelet-function analyser (PFA-100) were performed in all patients. All of the children in the study underwent a detailed physical examination and echocardiographic evaluation.Results:A history of bleeding was positive in 18% of the aortic stenosis group, 9% of the pulmonary stenosis group, and 4% of the control group. Seven of 60 (12%) patients had laboratory findings that implied a diagnosis of AVWS, and two of these (28%) had a history of bleeding. The frequency of AVWS was 14% in patients with aortic stenosis and 9% in those with pulmonary stenosis.Conclusion:AVWS is not rare in stenotic obstructive cardiac diseases. A detailed history of bleeding should be taken from patients with valvular disease. Even if the history is negative, whole blood count, PT and aPTT should be performed. If necessary, PFA-100 closure time and further tests should be planned for the diagnosis of AVWS.