BACKGROUND We intended to find the mutations of von Willebrand factor (VWF) gene as the most important contributing factor of von Willebrand disease (VWD) in Korean patients. METHODS In 40 known vWD patients mutations of vWF gene were sought by direct sequencing of PCR products targeting exons 18, 19, 20, 26, 28 and 52 frequently implicated as the locations of mutation. For factors other than VWF gene contributing to VWD phenotype, we tested ABO blood group and measured ADAMTS13 activity in VWD patients. RESULTS Twenty-seven cases (67.5%) were type 1 vWD, 3 cases (7.5%) type 3, and 5 cases (12.5%) type 2A. Three cases were type 2A or 2B (7.5%) and 2 cases were suspected to be type 2N (5.0%). Among them six candidate missense mutations were found: V1279I, R1306W, R1308C, and V1316M were previously reported in type 2B and type 1 vWD, and C858W and T1477I were novel findings. All patients were heterozygotes. Blood group O was overly represented in VWD patients, while ADAMTS13 activity of the patients was not significantly different from that of normal control. CONCLUSIONS Mutation of VWF gene detected by genetic studies can significantly improve the diagnostic accuracy, especially in subtype assignment of VWD. Two novel mutations, C858W and T1477I associated with VWD were found and expected to contribute to the elucidation of its pathophysiology.