A very rare case with coincidental idiopathic thrombocytopenic purpura (ITP) and familial von Willebrand disease (vWD) was reported. A 23-year-old female was admitted because of unusual bleeding tendency lasting still after the remission of thrombocytopenic state associated with ITP. Coagulation studies indicated the presence of a mild vWD, which was thought to be responsible for the bleeding tendency. The qualitative analysis of von Willebrand factor by crossed immunoelectrophoresis and SDS-1.2% agarose gel electrophoresis showed normal multimeric composition compatible with type I vWD. vWF-inhibitor was negative, and family study revealed that her mother was also affected with type I vWD. These results suggested that there was no immediate causal relation between the two disease states. The prevalence of concomitant disease states with ITP and vWD was discussed.